Chapter 15 – SQL Authorizationid

In this chapter, we’ll describe SQL <AuthorizationID>s in detail, and show you the syntax to use to create, alter and destroy them.

Table of Contents

<AuthorizationID>

We use the non-standart term <AuthorizationID> to mean a named bundle of Privileges, which is either a User or a Role. Users and Roles can be distinguished as follows.

  • A user is either an actual person or an application program that has access to SQL-data. Users are outside Schemas. If an <AuthorizationID> is a User, the methods used to create, drop, and map it to actual persons/application programs are implementation-defined.
  • A Role generally refers to a title or a set of duties within an organization. Roles are inside Schemas. If an <AuthorizationID> is a Role, it is created and dropped using standard SQL statements.

All <AuthorizationID>s must be unique within the SQL-environment.

The Objects that may belong to a User or a Tole are called Privileges; they depend on some <AuthorizationID>. An <AuthorizationID> may have the use of zero or more Privileges.

User

A User is either an actual person or an application program that has access to SQL-data.

[NON-PORTABLE] SQL does not include any CREATE USER, MAP USER, or DROP USER statements. The methods you´ll use with your DBMS to create and drop Users and to identify the real-life user an <AuthorizationID> represents are non-standart because the SQL Standart requires implementors to define how a User comes into being, how it may be destroyed, how it maps to users of SQL-data, and what constitutes a valid <AuthorizationID>. [OCELOT Implementation] The OCELOT DBMS that comes with this book “creates” a User automaticallywhen its identifier is usedin a CONNECT statement, a CREATE SCHEMA statement, a MODULE statement, a SET SESSION AUTHORIZATION statement, or a GRANT statement. Users are “dropped” if they own no Onjects and all their Privileges have been revoked.

Role

Large organization may have hordes of users with the same Privileges on the same Objects. For instance, circulation assistants are all allowed to do the circulation process. In SQL-92, the solutions were unsatisfactory:

  • If each circulation assistant had a different <AuthorizationID>, then there were too many Objects in the Catalog and granting/revoking was a major chore.
  • If all circulation assistants had the same <AuthorizationID>, some other method had to be devised so that one could distinguish which assistant really did what.

In SQL3 there is a major improvement: Roles. An SQL Role is a named bundle of zero or more Privileges. Granting a Role to an <AuthorizationID> allows that <AuthorizationID> to use every Privilege granted to that Role. There is a many-to-many relationship between user <AuthorizationID>s and Roles: a user may be granted the use of many Roles and the use of the same Role may be granted to many user <AuthorizationID>s. The use of a Role may also be granted to another Role.

Types of <AuthorizationID>

An <AuthorizationID> is defined by a descriptor that contains three pieces of information:

  1. The <identifier> that is the name of the <AuthorizationID>.
  2. Whether the <AuthorizationID> identifies a User or a Role.
  3. A Privilege descriptor for every Privilege granted to the <AuthorizationID>. At any point in time, an <AuthorizationID> has the use of every Privilege granted to PUBLIC, every Privilege directly granted to that <AuthorizationID> and every Privilege granted to every Role that has been granted to that <AuthorizationID>. (Since a Role may be granted to another Role, all dependent Role Privileges are also available to the <AuthorizationID>.
  • The SQL-session <AuthorizationID> is the user <AuthorizationID> for an SQL-session. Initially, it is the user <AuthorizationID> that started a given SQL-session and is determined from the USER clause of the CONNECT statement. The SQL-session <AuthorizationID> may never be NULL – if the CONNECT ... USER clause names a Role instead of a user <AuthorizationID>, the SQL-session <AuthorizationID> is set to a default value by your DBMS. You can change the SQL-session <AuthorizationID> with the SET SESSION AUTHORIZATION statement. The user function SESSION_USER returns the value of the current SQL-session <AuthorizationID>.
  • The context of an SQL-session includes its current User and its current Role: together, they determine the Privileges available to execute SQL statements in the SQL-session and one of them is always the “current <AuthorizationID>”. Either one of current user or current Role may be NULL at any time, but they may not both be NULL at the same time – the non-null identifier is the SQL-session’s current <AuthorizationID>. At the beginning of every SQL-session, the current user is set to the value of the SQL-session <AuthorizationID> and the current Role is set to the Role that started the SQL-session – it is determined from the CONNECT statement: if CONNECT ... USER specifies a <Role name>, the Role identified by that <Role name> becomes the current Role; otherwise, the current Role is NULL. You can change the current role with the SET ROLE statement. The equivalent user functions CURRENT_USER and USER return the value of the current user <AuthorizationID>. The user function CURRENT_ROLE returns the value of the current Role <AuthorizationID>.
  • The Module <AuthorizationID> is the owner of a given Module and is the current <AuthorizationID> when the Module’s SQL procedures are executed. The Module <AuthorizationID> may either be specifically identified (in the MODULE statement) or it will default to the current SQL-session <AuthorizationID>.
  • The Schema <AuthorizationID> is the owner of a given Schema and may either be specifically identified (in the CREATE SCHEMA statement) or it will default to the current Module <AuthorizationID>, if there is one. If the Module you’re running doesn’t have an explicit owner either, the Schema <AuthorizationID> defaults to the current SQL-session <AuthorizationID>.
  • The current <AuthorizationID> is the <AuthorizationID> whose Privileges are checked prior to the execution of an SQL statement. If the current <AuthorizationID> doesn’t have the required Privilege to perform an operation on SQL-data, the SQL statement will fail. For direct SQL, the SQL-session <AuthorizationID> is always the current <AuthorizationID>.

To create a Role and grant its use to an initial <AuthorizationID>, use the CREATE ROLE statement. To destroy a Role, use the DROP ROLE statement. To grant Privileges to a user or a Role, or to grant the use of a Role to an <AuthorizationID>, use the GRANT statement. To revoke Privileges from a user or a Role, or to revoke the use of a Role from an <AuthorizationID>, use the REVOKE statement or the DROP ROLE statement. To change the current SQL-session <AuthorizationID>, use the SET SESSION AUTHORIZATION statement. And to change the current Role, use the SET ROLE statement.

If you want to restrict your code to Core SQL, don’t use Roles at all.

<AuthorizationID> Names

An <AuthorizationID> name is eiter a <User name> or a <Role name>. The required syntax for an <AuthorizationID> name is as follows:

<AuthorizationID> ::=
user name | <Role name>

An <AuthorizationID> is a <regular identifier> or a <delimited identifier>, no more than 128 octets long, that is unique (for all <AuthorizationID>s and Roles) within the Cluster it belongs to. Typically, an <AuthorizationID> is a Christian name (e.g., BOB or SAM, identifying a user) or a department name (e.g.: DOCUMENTATION, identifying a Role) and, most often, has a one-to-one relationship to some user (i.e.: each user has only one <AuthorizationID>).

The <regular identifier> – PUBLIC – is a valid <AuthorizationID> only in the GRANT statement and the REVOKE statement. PUBLIC is the SQL special grantee, used as an “all-purpose” grantee, to enable system-wide Privileges to be granted to and/or revoked from all current and future <AuthorizationID>s with a single SQL statement. Every <AuthorizationID> always has the use of every Privilege granted to PUBLIC. The <delimited identifier> – "PUBLIC" – is never a valid <AuthorizationID>.

The <delimited identifier> – "_SYSTEM" – is a valid <AuthorizationID> only when you’re looking at INFORMATION_SCHEMA. "_SYSTEM" is the SQL special grantor, used (by your DBMS) as an “all-purpose” grantor, to enable Object-wide Privileges to be granted to an <AuthorizationID> that creates an Object, or to revoke cascading, system-wide Privileges from an <AuthorizationID> that drops an Object. (In the case of a DROP, "_SYSTEM" is also the grantee that revokes all related Privileges from all other <AuthorizationID>s.)

[NON-PORTABLE] Except for the cases (PUBLIC, "PUBLIC", "_SYSTEM") noted earlier, what your DBMS will recognize as a valid <AuthorizationID> is non- standard because the SQL Standard requires implementors to define what a valid <AuthorizationID> is. [OCELOT Implementation] The OCELOT DBMS that comes with this book will accept any SQL_TEXT <identifier> as an <AuthorizationID>.

CREATE ROLE Statement

The CREATE ROLE statement defines new Role. The required syntax for the CREATE ROLE statement is:

CREATE ROLE <Role name> [ WITH ADMIN <grantor> ]

   <grantor> ::= CURRENT_USER | CURRENT_ROLE

The CREATE ROLE statement specifically defines an <AuthorizationID> to be a Role, rather than a user: this is necessary since otherwise your DBMS could mistake <Role name> for a user name which appears in similar contexts. <Role name> is an <AuthorizationID> that is unique within your SQL-environment and CREATE ROLE automatically grants the use of the new Role to the current <AuthorizationID> WITH ADMIN OPTION (that is, the current <AuthorizationID> gets the use of the new Role and may pass this use on to others).

[NON-PORTABLE] Whether you can use CREATE ROLE is non-standard because the SQL Standard requires implementors to define what Privilege (if any) is needed to execute CREATE ROLE.

The optional WITH ADMIN clause decides which <AuthorizationID> (either the current user or the current Role) gets the use of this Role: CURRENT_USER is the <AuthorizationID> of the current user and CURRENT_ROLE is the <AuthorizationID> of the current Role. If you omit the clause, it defaults to WITH ADMIN CURRENT_USER – but if CURRENT_USER is NULL, the clause defaults to WITH ADMIN CURRENT_ROLE. If you specify WITH ADMIN CURRENT_USER and the current <AuthorizationID> is a <Role name>, or if you specify WITH ADMIN CURRENT_ROLE and the current <Role name> is NULL, the GRANT statement will fail: your DBMS will return the SQLSTATE error 0L000 "invalid grantor". Here are two examples:

CREATE ROLE assistants_role WITH ADMIN CURRENT_USER;
-- creates a Role, identified by the <AuthorizationID> ASSISTANTS_ROLE, for the current user

CREATE ROLE assistants_role WITH ADMIN CURRENT_ROLE;
-- creates a Role, identified by the <AuthorizationID> ASSISTANTS_ROLE, for the current Role

If you want to restrict your code to Core SQL, don’t use the CREATE ROLE statement.

Privilege

An SQL Privilege allows an <AuthorizationID> to perform a given action on a specific Table, Column, Domain, Character set, Collation, Translation, Trigger, SQL-invoked routine or UDT. Privileges are dependent on some <AuthorizationID> or Role, are created and granted with the GRANT statement and are destroyed with the REVOKE statement and the DROP ROLE statement. A Privilege is defined by a descriptor that contains five pieces of information:

  1. The name of the Object that the Privilege acts on.
  2. The <AuthorizationID> that granted the Privilege.
  3. The <AuthorizationID> that may use the Privilege.
  4. The action (either INSERT, UPDATE, DELETE, SELECT, REFERENCES, USAGE, UNDER, TRIGGER or EXECUTE) that may be taken on the specified Object.
  5. Whether the Privilege is grantable by the grantee.
  6. Whether the Privilege also applies to subtables in a hierarchy (for SELECT only).

<privileges>

The required syntax for a Privilege specification is as follows.

<privileges> ::=
<object privileges> ON <Object name>

   <Object name> ::=
   [ TABLE ] <Table name> |
   DOMAIN <Domain name>  |
   CHARACTER SET <Character set name> |
   COLLATION <Collation name> |
   TRANSLATION <Translation name> |
   TYPE <UDT name> |
   <specific routine designator>

   <object privileges> ::=
   ALL PRIVILEGES |
   <action> [ {,<action>}... ]

      <action> ::=
      DELETE |
      SELECT [ (<Column name> [ {,<Column name>} ... ]) ] |
      INSERT [ (<Column name> [ {,<Column name>} ... ]) ] |
      UPDATE [ (<Column name> [ {,<Column name>} ... ]) ] |
      REFERENCES [ (<Column name> [ {,<Column name>} ... ]) ] |
      TRIGGER |
      UNDER |
      USAGE |
      EXECUTE

The Privilege specification specifies one or more Privileges for a specific Object. Not all Privileges are valid for every Object.

ALL PRIVILEGES is a shorthand: it means every Privilege the grantor has on “<Object name>”. If “<Object name>” identifies a temporary Table, ALL PRIVILEGES is the only valid Privilege specification. Here’s an example:

ALL PRIVILEGES ON TABLE Table_1

In theory, you could substitute ALL PRIVILEGES for USAGE or EXECUTE, but there’s never a good reason to do so. Traditionally, ALL PRIVILEGES substitutes for the combination of Table Privileges: SELECT, INSERT, UPDATE, DELETE and perhaps TRIGGER or REFERENCES. The closest analogous construct is the *in "SELECT * ...", then. And similar objections to using it apply:

  • You can’t tell by reading the SQL code what Privileges are in fact being granted.
  • Because ALL PRIVILEGES is a shorthand, it might mean something different the next time you use it (because somebody might have in the interim granted additional Privileges to the current user).
  • If the current user has only one Privilege, you will not be warned that all the other potentially applicable Privileges are not being granted.

You should prefer to be explicit about what you’re granting: if you depend on a complex system of defaults you’ll miss something. These considerations don’t apply to temporary Tables since, for them, ALL PRIVILEGES really does mean all of: SELECT, INSERT, UPDATE, DELETE, TRIGGER, REFERENCES.

A SELECT, INSERT, UPDATE, REFERENCES, DELETE or TRIGGER Privilege is called a Table Privilege: it allows the specified action on the entire Table named in the Privilege’s descriptor – including on any Columns that are subsequently added to that Table. You may not grant the TRIGGER Table Privilege on anything but a Base table. You may not grant the other Table Privileges on a declared LOCAL TEMPORARY Table, or on any other Object. Note that the <keyword> TABLE is noise; it may be omitted from the Privilege specification. Here are two equivalent examples:

DELETE ON TABLE Table_1
DELETE ON Table_1

Both of these Privilege specifications define a Privilege that deletes rows from TABLE_1. Here’s an example of a Privilege specification that defines a Privilege that selects values from every Column of TABLE_1:

SELECT ON TABLE Table_1

And here’s an example of a Privilege specification that defines a Privilege that enables a Trigger to operate on every Column of TABLE_1:

TRIGGER ON TABLE Table_1

A SELECT (<Column name> list), INSERT (<Column name> list), UPDATE (<Column name> list) or REFERENCES (<Column name> list) is called a Column Privilege: it allows the specified action only on the Columns actually named when the Privilege is granted. You may not grant Column Privileges on the Columns of a declared LOCAL TEMPORARY Table or on any other Object. Again, the <keyword> TABLE is noise; it may be omitted from the Privilege specification. Here are two equivalent examples:

UPDATE(column_1,column_3) ON TABLE Table_1
UPDATE(column_1,column_3) ON Table_1

Both of these Privilege specifications define a Privilege that updates the values of TABLE_1.COLUMN_1 and TABLE_1.COLUMN_3. Here’s an example of a Privilege specification that defines a Privilege that inserts values into TABLE_1.COLUMN_2:

INSERT(column_2) ON TABLE Table_1

And here’s an example of a Privilege specification that defines a Privilege that enables TABLE_1.COLUMN_3 to be named in a Constraint or Assertion definition:

REFERENCES(column_3) ON TABLE Table_1

Every Privilege you have on a Table that is the basis for an updatable View is also granted to you on that View. For example, if you have the INSERT and SELECT Privileges on a Table and create an updatable View based on that Table, you will also have the INSERT and SELECT Privileges on the View. If your Table Privileges are grantable Privileges, your Privileges on the View will also be grantable.

An UNDER Privilege may either apply to a structured type or it may apply to a typed Table. An UNDER Privilege on a UDT allows the creation of subtypes; an UNDER Privilege on a typed Table allows the creation of subtables. YOu may not grant an UNDER Privilege on any other Object. Here’s an example:

UNDER ON TYPE bob.bob_udt

A USAGE Privilege allows the use of the Domain, UDT, Character set, Collation or Translation named in the Privilege’s descriptor. You may not grant a USAGE Privilege on any other Object. Here’s two examples:

USAGE ON DOMAIN domain_1
USAGE ON CHARACTER SET bob.charset_1

When a Catalog is “created”, your DBMS grants the USAGE Privilege on all INFORMATION_SCHEMA Character sets, Collations and Translations to PUBLIC WITH GRANT OPTION, so you always have the use of those Objects. If for some reason you should ever create a new character-related Object, do the same – there is no point being secretive here.

An EXECUTE Privilege allows the SQL-invoked routine named in the Privilege’s descriptor to be executed. You may not grant an EXECUTE Privilege on any other Object. Here’s an example:

EXECUTE ON SPECIFIC ROUTINE some_routine

(We define <specific routine designator> in our chapter on UDTs.)

Note that if two Privileges are identical except that one is a grantable Privilege and the other is not, the grantable Privilege takes precedence and both Privileges are set to grantable Privileges. Similarly, if two otherwise identical Privileges indicate one has WITH HIERARCHY OPTION and the other does not, the first takes precedence. Your DBMS will then eliminate the redundant duplicate Privilege.

If you want to restrict your code to Core SQL, don’t specify the UNDER Privilege, don’t specify the SELECT Privilege as a Column Privilege (that is, with a <Column name> list) and don’t specify the INSERT Privilege as a Column Privilege.

GRANT statement

The GRANT statement defines both Privilege grants and Role authorizations and so has two different syntaxes. The first is identified as the <grant privilege statement> and the second as the <grant role statement>.

<grant privilege statement>

The required syntax for the <grant privilege statement> form of the GRANT statement is:

<grant privilege statement> ::=
GRANT <privileges> TO <grantee> [ {,<grantee>}... ] [ WITH GRANT OPTION ]
[ FROM <grantor> ]

   <grantee> ::= PUBLIC | <AuthorizationID>
   <grantor> ::= CURRENT_USER | CURRENT_ROLE

The <grant privilege statement> grants one or more Privileges on a given Object to one or more grantees, including (possibly) PUBLIC. The grantor of the Privileges must, of course, hold those Privileges as grantable Privileges.

We’ve already shown you the syntax for the <privileges> Privilege specification; it’s used exactly that way in this form of the GRANT statement. Here are some examples:

GRANT SELECT ON TABLE Table_1 TO PUBLIC;
GRANT INSERT(column_1,column_5) ON Table_1 TO sam;
GRANT ALL PRIVILEGES ON TABLE Table_1 TO PUBLIC, bob, sam;
GRANT USAGE ON DOMAIN domain_1 TO bob;
GRANT EXECUTE ON SPECIFIC ROUTINE some_routine TO sam;

If your <grantee> is PUBLIC, you’re granting the Privilege to a list of <grantee>s that contains all of the <AuthorizationID>s in the Cluster – now and in the future. If your <grantee> is one or more <AuthorizationID>s, you’re granting the Privilege only to those <AuthorizationID>s. (Remember that an <AuthorizationID> may identify either a user or a Role.)

When you grant a SELECT, UPDATE or REFERENCES Table Privilege on a Base table that has subtables, the effect is two-fold:

The optional WITH HIERARCHY OPTION clause may apply only to a SELECT TABLEPrivilege that is granted on a typed Table. When you use this option, you are granting the SELECT Privilege not only on the Table named, but also on all of that Table´s substables.

The optional FROM clause names the grantor of the Privileges: CURRENT_USER is the <AuthorizationID> of the current user and CURRENT_ROLE is the <AuthorizationID> of the current Role. If you omit the clause, it defaults to FROM CURRENT_USER – but if CURRENT_USER is NULL, the clause defaults to FROM CURRENT_ROLE. If you specify FROM CURRENT_USER and the current <AuthorizationID> is a <Role name>, or if you specify FROM CURRENT_ROLE and the current <Role name> is NULL, the GRANT statement will fail: your DBMS will return the SQLSTATE error 0L000 "invalid grantor". Here are two examples:

GRANT UPDATE(column_1,column_5) ON Table_1 TO sam FROM CURRENT_USER;
GRANT DELETE ON Table_1 TO PUBLIC FROM CURRENT_ROLE;

The optional WITH GRANT OPTION clause defines a grantable Privilege: one that the grantee may, in turn, grant to other <AuthorizationID>s. If you omit the clause, the grantee will not be able to pass the Privilege on to others. Here are two examples:

GRANT REFERENCES(column_4,column_5) ON Table_1 WITH GRANT OPTION
   TO bob,sam FROM CURRENT_USER;
GRANT TRIGGER Table_1 WITH GRANT OPTION
   TO PUBLIC FROM CURRENT_ROLE;

If the GRANT statement isn’t able to successfully create a Privilege descriptor for every one of its Privilege specifications, your DBMS will return the SQLSTATE warning 01007 "warning-privilege not granted".

If you want to restrict your code to Core SQL, don’t use the FROM <grantor> clause or the WITH HIERARCHY OPTION with the GRANT statement.

<grant role statement>

The required syntax for the <grant role statement> form of the GRANT statement is:

<grant role statement> ::=
GRANT <Role name> [ {,<Role name>}... ] TO <grantee> [ {,<grantee>}... ]
[ WITH ADMIN OPTION ]
[ FROM <grantor> ]

   <grantee> ::= PUBLIC | <AuthorizationID>
   <grantor> ::= CURRENT_USER | CURRENT_ROLE

The <grant role statement> grants the use of one or more Roles to one or more grantees, including (possibly) PUBLIC. The grantor of the Roles must, of course, hold those Roles as grantable Roles (that is, WITH ADMIN OPTION).

If your <grantee> is PUBLIC, you’re granting the use of <Role name> to a list of <grantee>s that contains all of the <AuthorizationID>s in the Cluster – now and in the future. If your <grantee> is one or more <AuthorizationID>s, you’re granting the use of the Role only to those <AuthorizationID>s. Keep in mind that an <AuthorizationID> may identify either a user or a Role – this means you can grant the use of a Role not only to a user, but to another Role. Be careful with this last option: SQL doesn’t allow you to grant the use of a Role to a Role that already has the use of that Role – that is, no cycles of Role grants are allowed. Note that if two Role grants are identical except that one is a grantable Role and the other is not, the grantable Role takes precedence and both Roles are set to grantable Roles. Your DBMS will then eliminate the redundant duplicate Role grant.

The optional FROM clause names the grantor of the Roles: CURRENT_USER is the <AuthorizationID> of the current user and CURRENT_ROLE is the <AuthorizationID> of the current Role. If you omit the clause, it defaults to FROM CURRENT_USER – but if CURRENT_USER is NULL, the clause defaults to FROM CURRENT_ROLE. If you specify FROM CURRENT_USER and the current <AuthorizationID> is a <Role name>, or if you specify FROM CURRENT_ROLE and the current <Role name> is NULL, the GRANT statement will fail: your DBMS will return the SQLSTATE error 0L000 "invalid grantor". For example, in this SQL statement, the current user is granting the use of the ASSISTANTS_ROLE Role to every <AuthorizationID>:

GRANT assistants_role TO PUBLIC FROM CURRENT_USER;

In this following SQL statement, the current Role is granting the use of the ASSISTANTS_ROLE and the BOSSES_ROLE Role to the bob and joe <AuthorizationID>s:

GRANT assistants_role, bosses_role TO bob, joe FROM CURRENT_ROLE;

The optional WITH ADMIN OPTION clause defines a grantable Role: one that the grantee may, in turn, grant the use of to other <AuthorizationID>s. If you omit the clause, the grantee will not be able to pass the use of the Role on to others. Here are two examples:

GRANT assistants_role TO PUBLIC FROM CURRENT_USER WITH ADMIN OPTION;

GRANT assistants_role, bosses_role TO bob, joe
  FROM CURRENT_ROLE WITH ADMIN OPTION;

If you want to restrict your code to Core SQL, don’t use the <grant role statement> form of the GRANT statement and don’t grant any grantable Privileges on your Objects to others users – Core SQL only allows the owner of an Object to hold a grantable Privilege.

Data Control

You need explicit permission to perform any action on any SQL Object. SQL’s security system is discretionary (meaning that your rights vary depending on the action and on the Object). If you try to violate security, what usually happens is an error message. It’s not a sophisticated system, but there is some complexity when we get into details and definitions. Here’s a simple GRANT statement:

GRANT INSERT                           -- action
  ON  Books                            -- Object
  TO  joe;                             -- user

After this SQL statement is executed, the user named joe will be able to use the INSERT statement on the Table named Books. SQL’s security system boils down to this: you can let people access data with GRANT statements, or you can refuse to do so. The combination {action plus Object} is a Privilege. The action is usually a verb, the Object is usually a Table and the user is usually a person.

Action and Object

What action is possible depends on what the Object is. Here is a chart of the Object types which can be in GRANT statements, and the applicable actions for them:

OBJECT ACTION(S)
Base table
SELECT, INSERT, UPDATE, DELETE, TRIGGER,

REFERENCES
View SELECT, INSERT, UPDATE, DELETE, REFERENCES
Column SELECT, INSERT, UPDATE, REFERENCES
Domain USAGE
Character Set USAGE
Collation USAGE
Translation USAGE
SQL-invoked routine EXECUTE
UDT UNDER

Except for USAGE, the GRANT actions correspond to verbs that are used in SQL statements, for example:

UPDATE Integer_Tables SET
   integer_1 = CAST('1' AS INFORMATION_SCHEMA.CARDINAL_NUMBER);

For this SQL statement to be possible, the current <AuthorizationID> must have the following Privileges:

  • The UPDATE Privilege on Table INTEGER_TABLES and/or the UPDATE Privilege on Column INTEGER_TABLES.INTEGER_1.
  • The USAGE Privilege on Domain INFORMATION_SCHEMA.CARDINAL_NUMBER.

User/Role

A user is an <AuthorizationID>. It’s important to remember that users are outside the “database” – the effect is that <AuthorizationID>s are unqualified names, that there are no CREATE USER / DROP user statements in standard SQL and that some important questions depend on your operating system. An easy way to appreciate this is to remember that joe is still joe even if you switch to a different Schema in a different Catalog. Other points about users:

  • All DBMS operations are done on behalf of some user.
  • All Objects are owned by some user.
  • <AuthorizationID>s refer to real-world entities like people (Sam Brown / Joe) or jobs (VP Marketing / Tellers) or departments (Acquisitions / Front Office) or robots (Consolidate Report program, Internet spider). DBMSs can’t distinguish between these categories.

In a security context, we’re concerned with the user’s authorization to ask for certain acts to be performed. That’s where the GRANT statement comes in.

Owners

Consider this SQL statement:

CREATE SCHEMA Sally_Schema AUTHORIZATION Sally
   CREATE Table Sally_Dates (date_1 DATE, date_2 DATE);

(The question “who may execute a CREATE SCHEMA statement?” is a tough one. It’s implementor-defined, which might mean “anybody at all”, but more likely means “some special database administrator who exists when you first install the DBMS”. Though the question is important, it rarely is going to come up.)

In this example, a Role named Sally is the owner of SALLY_SCHEMA. Therefore, by definition, Sally is the owner of all Objects within that Schema – right now, this includes Table SALLY_DATES and the Columns DATE_1 and DATE_2.

Caution

You’ll often hear that the “owner of a Table” is “the user who created the Table”. Technically that’s wrong. Suppose another user, Joe, was able to create a Table and store it in Sally’s schema:

CREATE Table Sally_Schema.Joe_Dates (
   date_1 DATE, date_2 DATE);

Joe is the creator of Table JOE_DATES – but the owner is Sally, because Sally owns the Schema. The distinction between creators and owners is trivial for SQL-92 users because it is illegal to create Objects in a Schema that you don’t own. It is legal in SQL3, though – so don’t let old definitions mix you up.

As the Schema owner, Sally now has the power to CREATE, ALTER or DROP all Objects in the Schema. Sally alone has this power – she cannot delegate it – so a Schema owner’s CREATE/ALTER/DROP power is a right, not a Privilege. This power exists, but we will not trouble with it further because it does not involve the GRANT statement.

Sally also has a full set of all Privileges that apply for each Object in her Schema. For example, Sally has the USAGE Privilege for all of her Schema’s Domains, Character sets, Collation and Translations and she has SELECT, UPDATE, INSERT, DELETE, REFERENCES and TRIGGER Table Privileges for all of her Schema’s Base Tables. Sally’s set of Privileges stems automatically from her ownership of the Schema. Technically it is considered that she was “granted” these powers by a pseudo-user named "_SYSTEM", but for practical purposes she is the ultimate authority. She cannot lose her right to do these operations. She can, however, pass on any or all of her Privileges to any other user. This ability is called the GRANT OPTION, because Sally has the option of granting the Privileges she holds. Sally also may pass on the the Privileges she holds. Sally also may pass on the grant option itself. grant option itself.

GRANTs on Tables

Let’s follow what a DBMS does with a GRANT statement, using a series of examples based on SALLY_SCHEMA. Here’s a GRANT statement for that Schema (assume Sally is the current <AuthorizationID>):

GRANT SELECT, INSERT ON Sally_Dates TO joe WITH GRANT OPTION;

Given this SQL statement, a DBMS acts as follows:

  • It determines that Sally owns the Schema, therefore she has a full set of Privileges on Table SALLY_DATES. There is no need to find a Privilege descriptor to see whether she may grant Privileges.
  • It determines that Joe does not exist, so it silently creates a user named Joe. Even if Joe has not made his existence known before, that would be no reason to believe he does not exist. (We’re making some assumptions here for the sake of the example. This would be the usual case, but your DBMS might require you to execute some form of (non-standard) CREATE USER statement or it may have some operating-system dependent check on whether Joe exists.)
  • It creates these six new Privilege descriptors:
GRANTOR GRANTEE OBJECT NAME ACTION GRANT_OPTION
Sally Joe Table Sally_Dates SELECT YES
Sally Joe Table Sally_Dates INSERT YES
Sally Joe Column date_1 SELECT YES
Sally Joe Column date_1 INSERT YES
Sally Joe Column date_2 SELECT YES
Sally Joe Column date_2 INSERT YES

The four “Column Privilege” descriptors may surprise you a bit since the GRANT statement syntax doesn’t include COLUMN as an Object. But since it does allow Column Privileges to be defined, the effect is that a GRANT on a Table creates, not only a Privilege descriptor for that Table, but also a Privilege descriptor for every applicable Column of that Table.

Now, suppose that time passes and the current <AuthorizationID> becomes Joe, who executes this GRANT statement:

GRANT INSERT, UPDATE ON Sally_Dates TO Sam;

Given this SQL statement, a DBMS acts as follows:

  • It determines that Joe does not own the Schema, so it looks through the Privilege descriptors to see if there are any where grantee = ‘Joe’, Object = ‘Table’, Name = ‘Sally_Dates’ and grant_option = YES. It finds INSERT Privileges but it does not find UPDATE Privileges, so it returns the SQLSTATE warning 01007 "warning-privilege not granted" and it creates these three new Privilege descriptors:
GRANTOR GRANTEE OBJECT NAME ACTION GRANT_OPTION
Joe Sam Table Sally_Dates INSERT NO
Joe Sam Column date_1 INSERT NO
Joe Sam Column date_1 INSERT NO

More time passes and Sally is once again the current <AuthorizationID>. She does the following:

GRANT INSERT ON Sally_Dates TO Sam;
GRANT INSERT(date_1) ON Sally_Dates TO bob;

Given this SQL statement, a DBMS acts as follows:

  • Once again it sees that Sally owns the Schema and so has full Privileges, all grantable.
  • It creates these five new Privilege descriptors:
GRANTOR GRANTEE OBJECT NAME ACTION GRANT_OPTION
Sally Sam Table Sally_Dates INSERT NO
Sally Sam Column date_1 INSERT NO
Sally Sam Column date_2 INSERT NO
Sally Bob Table Sally_Dates INSERT NO
Sally Bob Column date_1 INSERT NO

These Privilege descriptors for Same are not duplicates of the ones that were created earlier, when Joe granted Sam the same Privileges, therefore the DBMS makes new Privilege descriptors. Later, however, Sally repeats this GRANT:

GRANT INSERT ON Sally_Dates TO Sam;

In this final case, nothing happens: there are already Privilege descriptors with the same {grantor, grantee, Object, name, action} and duplicates will not be added to INFORMATION_SCHEMA. Your DBMS will return “okay” after creating zero new rows.

A related example – trivial but worth making because older SQL books describe it incorrectly – concerns the question: what if the last example had contained the WITH GRANT OPTION clause? In that case, the grant_option field for the last two Privilege descriptors would have been changed from NO to YES.

In the end, we have fourteen new Privilege descriptors. Sally has the same powers of ownership as before, Joe can INSERT INTO Sally_Dates or SELECT FROM Sally_Dates, Sam can INSERT INTO Sally_Dates and Bob can INSERT INTO Sally_Dates.date_1. Joe’s Privileges are WITH GRANT OPTION, Sam’s and Bob’s are not. We have been at some pains to show that the result is both Table and Column Privilege descriptors, and no two Privilege descriptors can be exact duplicates. There can, however, be considerable overlap, as is seen by the fact that Sam has two sets of INSERT Privileges on the same Object – one with grantee=Sally and the other with grantee=Joe.

Caution

it is a delusion to believe that Bob may now execute this SQL statement:

INSERT INTO Sally_Dates (date_1) VALUES (CURRENT_DATE);

because to do this, Bob needs the INSERT Privilege for both Column DATE_1 and Column DATE_2 -- INSERT statements create whole rows. So it’s useless to "GRANT INSERT(Column-list)" unless (a) you expect that somebody else will grant access on the other Columns or (b) your (Column-list) contains the names of all Columns in the Table, but you don’t want to just "GRANT INSERT ON <Table name>" because that would give access not only to all Columns currently in the Table, but to all Columns which will ever be in the Table (including Columns added by future ALTER TABLE statements).

If Sally does the following:

GRANT UPDATE(date_1) ON Sally_Dates TO Sam;

the effect is that Sam can do this:

UPDATE Sally_Dates SET date_1 = 'DATE '1994-07-15';

but Sam can’t do this:

UPDATE Sally_Dates SET date_2 = 'DATE '1994-07-15';

There are times when such fine-tuning of controls is desirable. If Sally does the follwoing:

GRANT SELECT(date_1) ON Sally_Dates TO Sam;

the effect is that Sam can do this:

SELECT date_1 FROM Sally_Dates;

SELECT COUNT(*) FROM Sally_Dates;

but he can’t specifically SELECT the second Column.

Caution

If SELECT (Column-list) Privileges are granted, the recipients should avoid using "SELECT * ...". The "SELECT * ..." statement will suddenly cease to work for them if new Columns are added to the Table.

We would never recommend by-Column granting, without first looking at the alternative – granting on a View.

GRANTs on Views

By definition, a View is a Table. So the considerations specific to “GRANTs on Views” have nothing to do with syntax – the syntax is the same as for any Table – but with the effect. Specifically, let’s see what would occur if Joe owns a View of Table SALLY_DATES.

To make the example possible we have to start by giving Joe his own Schema. It’s convenient to make Joe’s View at the same time. Here’s the SQL statement to do it:

CREATE Schema Joe_Schema AUTHORIZATION Joe
   CREATE View Joe_Views AS
      SELECT date_1,date_2 FROM Sally_Schema.Sally_Dates;

To do this, Joe will need the SELECT Privilege on the Columns of Table SALLY_DATES in SALLY_SCHEMA – we gave these to him earlier. Naturally, the rules don’t let Joe gain new Privileges by owning a View. He can DROP this View (that’s his power as an owner and he can SELECT FROM or INSERT INTO this View (those are the grantable Privileges he holds on SALLY_DATES) – and that’s all. He cannot do this:

UPDATE Joe_Views SET date_1 = CURRENT_DATE;

because UPDATE is not a Privilege he holds on SALLY_DATES, and ultimately, an UPDATE on the View will UPDATE the Table. Now assume that Joe creates another View:

CREATE View Joe_Views_2 AS
   SELECT date_1 FROM Joe_Views WHERE date_1 > DATE '1994-01-03';

and then does a GRANT to Sam:

GRANT INSERT, SELECT ON Joe_Views_2 TO Sam;

… a beautiful example of why Views are useful for security systems. Here, Joe has restricted Sam’s access not only to a particular Column of a Table, but to particular rows of that Table. He has done more than is possible with by-Column granting – and he has done it more cleanly.

GRANTs on Procedures

The sad news is that the most useful GRANT of all is one that hardly anyone can use yet. It depends on the existence of procedures, which are an SQL3 Object. Only GRANTs on procedures can bring us real-word examples like the following one.

Think of a bank. Tellers in the bank do not have Privileges on Tables, or on Columns within Tables. If we give them UPDATE Privileges on customer accounts, they’ll be able to do anything at all to the accounts (too dangerous); if we don’t, they won’t be able to do anything at all (too restrictive). What everyone – managers, tellers and customers – wants is a Privilege that allows a specific combination of operations. For example, let Joe transfer money – that is, let him withdraw from one account and deposit to another account, provided that the total of the transaction balances out to $0.00. You could define this situation in a program using syntax like this:

CREATE PROCEDURE Transfer_Procedure
  ... INSERT
  ... UPDATE
  ... CHECK
  ... CASE
  ...;

And then you could allow Joe to use the procedure with:

GRANT EXECUTE ON Transfer_Procedure TO Joe;

Almost always, restricting based on an SQL verb (INSERT / UPDATE / DELETE) is vague. Administrators of non-imaginary institutions would prefer finer tuning: they want to restrict actions based on entire SQL statements or, more often, on combinations of SQL statements. Since procedure granting will give them that, eventually they’ll throw away the old grants on Tables / Columns / Views, and GRANT EXECUTE will become the norm.

Constraints

If a user names a Column within a Constraint or Assertion definition, that means he/she/it REFERENCES the Column. (Don’t be misled by the appearance of the <keyword> REFERENCES in FOREIGN KEY Constraint definitions; in this context we’re talking about any kind of Constraint. And don’t be misled by the appearance of the <keyword> SELECT inside some complex CHECK Constraints; the action here is REFERENCES so the SELECT Privilege is irrelevant for Constraints.) Here’s an example – Sally (who owns the Table SALLY_DATES) may issue this GRANT statement:

GRANT REFERENCES ON Sally_Dates TO Joe;

This means that Joe can now create a Constraint or Assertion that uses the Columns of SALLY_DATES – for example:

CREATE ASSERTION joe_constraint CHECK (
   Joe_Views.date_1 <> DATE '1999-12-31');

Not only does this Assertion limit the values of JOE_VIEWS, it also limits the values of SALLY_DATES, since that is the Table that the View is based on. Obviously, Joe should not be able to set limits on Sally’s data unless she specifically allows him to – thus, the REFERENCES Privilege.

REVOKE Statement

By the time we finish setting up a Catalog and granting appropriate Privileges to our users, we probably have several thousand Privilege descriptors in INFORMATION_SCHEMA – more than the count for all other Schema Objects combined. Maintaining them is made easier by the fact that when an Object is dropped, the DBMS will silently destroy all associated Privilege descriptors. That leaves only the problem: how do we adjust for the occasional necessity to remove a Privilege descriptor due to a change in status of a particular user (or Role)? The problem does not occur frequently, but can be mightily cumbersome: the SQL Standard devotes about 40 pages to it. We have managed to simplify the description somewhat, by focussing on the two “essentials” of the process:

  1. What we are trying to do is reverse the effects of a GRANT statement, using a REVOKE statement – the clauses of which have almost the same syntax as GRANT’s clauses.
  2. What we are really doing is deleting Privilege descriptor rows from INFORMATION_SCHEMA.

The REVOKE statement destroys both Privilege descriptors and Role authorizations and so has two different syntaxes. The first is identified as the <revoke privilege statement> and the second as the <revoke role statement>. The required syntax for the REVOKE statement is as follows.

<revoke privilege statement> ::=
REVOKE [ GRANT OPTION FOR ] <privileges> FROM <grantee> [ {,<grantee>}... ]
[ FROM {CURRENT_USER | CURRENT_ROLE} ] {RESTRICT | CASCADE}

<revoke role statement> ::=
REVOKE [ ADMIN OPTION FOR ] <Role name> [ {,<Role name>}... ]
FROM <grantee> [ {,<grantee>}... ]
[ FROM {CURRENT_USER | CURRENT_ROLE} ]
{RESTRICT | CASCADE}

   <grantee> ::= PUBLIC | <AuthorizationID>

The <revoke privilege statement> revokes one or more Privileges on a given Object from one or more grantees, including (possibly) PUBLIC, while the <revoke role statement> revokes the use of one or more Roles from one or more grantees. Only the grantor of the Privileges (or the Roles) may revoke them. We’ve already shown you the syntax for the <privileges> Privilege specification; it’s used exactly that way in the <revoke privilege statement> form of the REVOKE statement. Here are some examples:

REVOKE SELECT ON TABLE Table_1 FROM PUBLIC CASCADE;
REVOKE INSERT(column_1,column_5) ON Table_1 FROM sam CASCADE;
REVOKE ALL PRIVILEGES ON TABLE Table_1 FROM PUBLIC CASCADE;
REVOKE USAGE ON DOMAIN domain_1 FROM bob CASCADE;
REVOKE EXECUTE ON SPECIFIC ROUTINE some_routine FROM sam CASCADE;

And here’s an example of the <revoke role statement> form of REVOKE:

REVOKE assistants_role FROM PUBLIC CASCADE;

In both cases, if your <grantee> is PUBLIC, you’re revoking the Privilege (or the use of the Role) from a list of <grantee>s that contains all of the <AuthorizationID>s in the Cluster. If your <grantee> is one or more <AuthorizationID>s, you’re revoking the Privilege (or the use of the Role) only from those <AuthorizationID>s. (Remember that an <AuthorizationID> may identify either a user or a Role.)

Remember that, for Tables, GRANT creates Privilege descriptors for both the Table and its Columns. Well, when you REVOKE a Table Privilege, all by-Column Privileges for that Table disappear too. The effect is a bit strange: when you revoke a Table Privilege, you lose the Column Privilege (even if it was granted separately) and when you revoke a Column Privilege, you lose that Column Privilege – even if it resulted from a Table Privilege GRANT.

The optional FROM clause names the grantor of the Privileges or the Role you’re revoking: CURRENT_USER is the <AuthorizationID> of the current user and CURRENT_ROLE is the <AuthorizationID> of the current Role. If you omit the clause, it defaults to FROM CURRENT_USER – but if CURRENT_USER is NULL, the clause defaults to FROM CURRENT_ROLE. If you specify FROM CURRENT_USER and the current <AuthorizationID> is a <Role name>, or if you specify FROM CURRENT_ROLE and the current <Role name> is NULL, the REVOKE statement will fail: your DBMS will return the SQLSTATE error 0L000 "invalid grantor". Here are two examples:

 REVOKE UPDATE ON Table_1 FROM sam FROM CURRENT_USER CASCADE;
 -- revokes the UPDATE Privilege on TABLE_1 from Sam only if the current user granted that Privilege in the first place

 REVOKE assistants_role FROM PUBLIC FROM CURRENT_ROLE CASCADE;
-- revokes the use of the ASSISTANTS_ROLE Role from PUBLIC only if the current Role granted the use of that Role in the first place

The optional HIERARCHY OPTION FOR clause (applicable only to the <revoke privilege statement>) allows you to revoke only the WITH HIERARCHY OPTION from the specified SELECT Privilege.

The optional GRANT OPTION FOR (<revoke privilege statement>) and ADMIN OPTION FOR (<revoke role statement>) clauses allow you to revoke only the grantability of a Privilege or a Role. For example, consider these SQL statements:

GRANT UPDATE ON TABLE Table_1 TO sam WITH GRANT OPTION;
REVOKE GRANT OPTION FOR UPDATE ON Table_1 FROM sam CASCADE;

The first SQL statement allows Sam to update TABLE_1, and to pass this Privilege on to others. The second SQL statement revokes the latter ability: Sam can still update TABLE_1, but may no longer pass the Privilege on. Here’s another example:

GRANT assistants_role TO bob WITH ADMIN OPTION;
REVOKE WITH ADMIN OPTION FOR assistants_role FROM bob CASCADE;

The first SQL statement allows Bob to use all of the Privileges belonging to the ASSISTANTS_ROLE Role, and to pass the use of this Role on to others. The second SQL statement revokes the latter ability: Bob can still use the Role’s Privileges, but may no longer pass that use on.

The GRANT/ADMIN option clauses have another effect. Suppose that a user holds a Privilege on a Table WITH GRANT OPTION, and does so, also with GRANT OPTION. The second user can now do the same for a third user, and so on – for example:

GRANT DELETE ON TABLE Sally_Dates TO joe WITH GRANT OPTION;
-- assume Sally does this

GRANT DELETE ON TABLE Sally_Dates TO sam WITH GRANT OPTION;
-- assume Joe does this

GRANT DELETE ON TABLE Sally_Dates TO bob WITH GRANT OPTION;
-- assume Sam does this

What should happen if Sally now does the following?

REVOKE DELETE ON TABLE Sally_Dates FROM joe;

Here, we’ve deliberately left off RESTRICT/CASCADE for the sake of the example, so let’s assume that the SQL statement works: Joe no longer has the DELETE Privilege on SALLY_DATES. The Privileges handed down from Joe to Sam, and from Sam to Bob, are now called “abandoned Privileges”: they are dependent on Joe’s DELETE Privilege – and Joe doesn’t have it any more. This is where the RESTRICT/CASCADE <keyword>s come in.

  • If your REVOKE statement specifies CASCADE, the REVOKE succeeds – and it cascades down to revoke any Privileges that would otherwise be abandoned. In our example, that means both Sam and Bob would no longer have the DELETE Privilege on SALLY_DATES either.
  • If your REVOKE statement specifies RESTRICT, the REVOKE succeeds only if the Privilege being revoked has no dependent Privileges. In our example, that means the REVOKE statement would fail.

The same holds true for revoking the use of a Role.

Objects can also become “abandoned” when a Privilege or the use of a Role is revoked. For example, remember that Joe holds the SELECT Privilege on SALLY_DATES and, with this, was able to create his View, JOE_VIEWS. Now suppose Sally does this:

REVOKE SELECT ON Sally_Dates FROM joe CASCADE;

The effect is that, not only does Joe lose his ability to SELECT from SALLY_DATES, but that JOE_VIEWS is dropped! The reason is that, in effect, JOE_VIEWS is nothing but a SELECT that Joe does from SALLY_DATES, and since such SELECTs are no longer allowed, the View may no longer exist. If, on the other hand, Sally does the following:

REVOKE SELECT ON Sally_Dates FROM joe RESTRICT;

the effect is that the REVOKE statement fails: Sally may not revoke Joe’s ability to SELECT from SALLY_DATES because this would mean that JOE_VIEWS would be abandoned – and this is not allowed. The same holds true for any Object that anyone was able to create only because they held some required Privilege (or were able to use a Role that held that Privilege): if REVOKE ... RESTRICT is used, the statement will fail but if REVOKE ... CASCADE is used, the statement will not only revoke but drop all Objects that would otherwise be abandoned.

If the REVOKE statement isn’t able to find a Privilege descriptor for every one of its Privilege specifications, your DBMS will return the SQLSTATE warning 01006 "warning-privilege not revoked".

If you want to restrict your code to Core SQL, don’t use the <revoke role statement> form of the REVOKE statement and don’t use REVOKE ... CASCADE or the GRANT OPTION FOR or HIERARCHY OPTION FOR clause. Also, when revoking, make sure that your current <AuthorizationID> is the owner of the Schema that owns the Object you’re revoking Privileges for.

DROP ROLE Statement

The DROP ROLE statement destroys a Role. The required syntax for the DROP ROLE statement is:

DROP ROLE <Role name>

The <Role name> must identify an existing Role for which an enabled <AuthorizationID> has the WITH ADMIN OPTION. That is, only an <AuthorizationID> with the WITH ADMIN OPTION on a Role may drop it. The effect of DROP ROLE <Role name>, e.g.,

DROP ROLE assistants_role;

is that the Role named ASSISTANTS_ROLE will be destroyed and that your DBMS will also do this for every <AuthorizationID> that was granted use of the Role:

REVOKE assistants_role FROM <AuthorizationID> RESTRICT;

If you want to restrict your code to Core SQL, don’t use the DROP ROLE statement.

What privileges do I have?

Earlier in this chapter, we said that every Privilege is defined by a descriptor stored in INFORMATION_SCHEMA. You can thus find out what Privileges you have by querying the appropriate Views therein (see our chapter on SQL Catalogs). Each “Privilege descriptor” View includes Columns for grantor, grantee, Object, <Object name> and is_grantable – the basic Privilege description stuff. You might think that this makes things fairly straightforward – but take note! There is deep trickiness implied by simple-sounding questions like: may Joe may SELECT from SALLY_DATES?

The first trickiness is that it is not enough to look for “Grantee = ‘Joe’”. Joe may have a Privilege due to his ROLE, and at any rate, Joe is a member of the PUBLIC. So when searching for Joe’s Privileges, the conditions should include “Grantee = 'PUBLIC' and Grantee = ‘whatever Role Joe may be able to use’”.

The second trickiness is that it is not enough to look for “Object = 'Sally_Dates' in the TABLE_PRIVILEGES View. Joe may have a Privilege on only one Column, so you have to search the COLUMN_PRIVILEGES View too. And even if you do find that Joe does have the SELECT Privilege, that might not be enough – he might also need separate USAGE Privileges for the UDT, the Character set and the Collation associated with each Column in the Table. And even if you find that Joe doesn’t have the SELECT Privilege, the answer may be insufficient – he might have the SELECT Privilege on a View of the Table, or he might be able to get all the data he needs using a procedure.

Tip

Explain these trickinesses to other users at your site, then ask them to observe these limits:

  • Number of by-Column GRANTs = 0.
  • Number of Roles = 1 (not including PUBLIC).
  • Number of Views = 1 per Table.
  • Number of USAGE GRANTs = 1 (that is, one GRANT only, to PUBLIC).

Violating the security system

Each of the following depends on a “hole” in the Standard SQL security wall. Perhaps the vendor of your particular DBMS hasn’t plugged the hole. What fun it would be to find out …

If you have the SELECT Privilege WITH GRANT OPTION on a single Table: Suppose the grantor of your Privilege is Sally. Why not reciprocate and GRANT your Privilege back to her? The advantage is that later, if Sally tries to revoke your Privilege and forgets to say CASCADE, she will fail because there is now a chain of Privilege descriptors, terminating with her.

If your database is stored on a local microcomputer: The DBMS can’t block your access to the file – usually its only line of defense is encryption or proprietary formatting (Microsoft Access and dBASE IV use variations of this defense). If you know what the Table and Column names are, you can go to another computer and make a database with the same structure but different data. Then copy your file over the legitimate one. This is a cuckoo’s egg violation.

If your database is stored on a distant server: There’s still a chance that the client receives complete row copies for local filtering. Start a long query, then turn your computer off. Start it up again and look for temporary unclosed files, probably in the windowstemp directory.

Here is a security hole that is opened up by the REFERENCES Privilege: Sally creates a Table –

CREATE TABLE Sally_1 ( column1 SMALLINT);

Sally lets Joe reference her Table –

GRANT REFERENCES ON Sally_1 TO joe;

Joe creates a Table –

CREATE TABLE Joe_1 (column_1 INT REFERENCES Sally_1);

Joe lets Sam update his Table –

GRANT UPDATE ON Joe_1 to Sam;

Now, even though Sam has no Privileges at all on Sally’s Table, he can find out what’s in it! All he has to do is:

UPDATE Joe_Schema.Joe_1 SET
   column_1 = :x;

in a loop, for “x” = all possible SMALLINT values. If, and only if, UPDATE succeeds, then the value of “x” is in Sally’s Table.

User Functions

The SQL Standard defines four types of <AuthorizationID> whose values can be obtained through the use of the scalar user functions USER, CURRENT_USER, SESSION_USER, SYSTEM_USER and CURRENT_ROLE: each returns an SQL_TEXT character string whose value represents an <AuthorizationID>.

[NON-PORTABLE] The result of a user function is non-standard because the SQL Standard requires implementors to define whether the result string is fixed length or variable length and the result string’s fixed length or maximum length (as applicable). [OCELOT Implementation] The OCELOT DBMS that comes with this book has each user function return a variable length SQL_TEXT string. The result has a maximum length of 128 octets.

The required syntax for a user function is as follows.

user function ::=
USER |
CURRENT_USER |
SESSION_USER |
SYSTEM_USER |
CURRENT_ROLE

A user function returns an SQL_TEXT character string with the COERCIBLE coercibility attribute.

CURRENT_USER returns the <AuthorizationID> of the current user. This is either the user specified in the CONNECT statement that began the SQL-session (assuming it was a user, and not a Role that began the session) or a default <AuthorizationID> set by your DBMS. CURRENT_USER will be NULL if the current <AuthorizationID> is a <Role name>. USER is a synonym for CURRENT_USER that may be used in Core SQL.

CURRENT_ROLE returns the <AuthorizationID> of the current Role. This is either the Role specified in the CONNECT statement that began the SQL-session (assuming it was a Role, and not a user that began the session; otherwise NULL) or the Role specified in the most recent SET ROLE statement issued for the SQL-session. CURRENT_ROLE will be NULL if the current <AuthorizationID> is a user, rather than a Role.

SESSION_USER returns the <AuthorizationID> of the SQL-session user. This is either the user specified in the CONNECT statement that began the SQL-session (assuming it was a user, and not a Role that began the session; otherwise a default <AuthorizationID> set by your DBMS) or the user specified in the most recent SET SESSION AUTHORIZATION statement issued for the SQL-session. In most cases, the SQL-session <AuthorizationID> is the same as the current <AuthorizationID>.

[NON-PORTABLE] SYSTEM_USER returns an <AuthorizationID> that represents the operating system user who executed the SQL-client Module that contains the SYSTEM_USER function call and is thus non-standard because the SQL Standard requires implementors to define their system user. [OCELOT Implementation] The OCELOT DBMS that comes with this book has a SYSTEM_USER called OCELOT.

The current <AuthorizationID> is the user or Role against which Privilege checking is done to see whether an SQL operation is allowable. For example, prior to executing this SQL statement:

SELECT * FROM Table_1;

your DBMS will check to see that the current <AuthorizationID> has the SELECT Privilege on that Table. If the current <AuthorizationID> has the Privilege, the SELECT is performed. If the current <AuthorizationID> does not have the Privilege, the SELECT is disallowed.

The SQL-session <AuthorizationID> is the <AuthorizationID> that is used as the default <AuthorizationID> whenever a SQL operation which requires an <AuthorizationID> is not provided with an explicit <AuthorizationID> specification. For example, when executing this SQL statement:

CREATE SCHEMA bob;

your DBMS effectively executes this SQL statement:

CREATE SCHEMA bob AUTHORIZATION SESSION_USER;

If you want to restrict your code to Core SQL, don’t use CURRENT_USER, SESSION_USER, SYSTEM_USER or CURRENT_ROLE.

Dialects

Many vendors have added their own Privileges to the SQL Standard’s set. For example:

  • IBM’s DB2 has a SYSADM (system administrator) who can CREATE and DROP in any Schema, and who can create Schemas (one of the implementor-defined areas in the Standard). Several other vendors also have similar “super user” Privileges which are not associated with any particular Object.
  • Sybase has a CONNECT Privilege; other vendors allow connection by anyone, but new users can’t do anything without further Privileges.
  • The most popular non-standard Privilege is GRANT ALTER (which sometimes allows users to both alter and drop Tables).
  • DBMSs which allow non-standard Objects allow non-standard Privileges to go with them; thus GRANT INDEX is common, and DB2 also has access controls for tablespaces and indexspaces (which are somewhat like “files”).

On the other hand, older DBMSs may fail to support the REFERENCES Privilege. They allow Constraints to be defined by anyone who has the appropriate SELECT Privileges instead.

A few SQL3 features are already fairly common. Sybase, Microsoft SQL Server and Informix allow “GRANT SELECT (Column-name list) …”. Oracle has had a CREATE ROLE statement since version 7.0; Sybase and Microsoft SQL Server also allow Roles but they use non-standard terms and syntax.

As for syntax – the majority of DBMSs will let you specify more than just one “Object” in both GRANT and REVOKE statements. This leads to ambiguities – what is "GRANT UPDATE(column1) ON Tables_1, Tables_2" supposed to do? And is it proper if the different Objects are in different Catalogs? And what if different Privileges apply for different Objects? You’re on safer ground if you just ignore this sort of enhancement.

The biggest variations involve the ways that the DBMS can identify and acknowledge users. If your operating system has a list of valid users and passwords (something you’ll notice if you have to “log in” to your computer), then your DBMS can get the user by querying the OS (Ingres, Informix and DB2 do this). Alternatively, or in addition, your DBMS might require you to supply both a user ID and a password when you CONNECT (Oracle and Sybase do this). In the former case, the user’s name is probably limited to as few as eight characters because the OS has more restrictions than the DBMS does. In the latter case, there is probably a non-standard CREATE USER statement and a “user” Object stored inside the database.

Finally, you will see some DBMSs skimping on their obligation to store Privilege descriptors for owners. A quick glance at the INFORMATION_SCHEMA.COLUMN_PRIVILEGES View should tell you whether your DBMS is one of these.