Information schema

information_schema is a special schema that contains virtual tables which are read-only and can be queried to get information about the state of the cluster.

Table of contents

Access

When the user management is enabled, accessing the information_schema is open to all users and it does not require any privileges.

However, being able to query information_schema tables will not allow the user to retrieve all the rows in the table, as it can contain information related to tables over which the connected user does not have any privileges. The only rows that will be returned will be the ones the user is allowed to access.

For example, if the user john has any privilege on the doc.books table but no privilege at all on doc.locations, when john issues a SELECT * FROM information_schema.tables statement, the tables information related to the doc.locations table will not be returned.

Virtual tables

tables

The information_schema.tables virtual table can be queried to get a list of all available tables and views and their settings, such as number of shards or number of replicas.

cr> SELECT table_schema, table_name, table_type, number_of_shards, number_of_replicas
... FROM information_schema.tables
... ORDER BY table_schema ASC, table_name ASC;
+--------------------+-------------------------+------------+------------------+--------------------+
| table_schema       | table_name              | table_type | number_of_shards | number_of_replicas |
+--------------------+-------------------------+------------+------------------+--------------------+
| doc                | galaxies                | VIEW       |             NULL | NULL               |
| doc                | locations               | BASE TABLE |                2 | 0                  |
| doc                | partitioned_table       | BASE TABLE |                4 | 0-1                |
| doc                | quotes                  | BASE TABLE |                2 | 0                  |
| information_schema | character_sets          | BASE TABLE |             NULL | NULL               |
| information_schema | columns                 | BASE TABLE |             NULL | NULL               |
| information_schema | key_column_usage        | BASE TABLE |             NULL | NULL               |
| information_schema | referential_constraints | BASE TABLE |             NULL | NULL               |
| information_schema | routines                | BASE TABLE |             NULL | NULL               |
| information_schema | schemata                | BASE TABLE |             NULL | NULL               |
| information_schema | sql_features            | BASE TABLE |             NULL | NULL               |
| information_schema | table_constraints       | BASE TABLE |             NULL | NULL               |
| information_schema | table_partitions        | BASE TABLE |             NULL | NULL               |
| information_schema | tables                  | BASE TABLE |             NULL | NULL               |
| information_schema | views                   | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_am                   | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_attrdef              | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_attribute            | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_class                | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_constraint           | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_database             | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_description          | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_enum                 | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_index                | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_namespace            | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_proc                 | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_range                | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_roles                | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_settings             | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_stats                | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_tablespace           | BASE TABLE |             NULL | NULL               |
| pg_catalog         | pg_type                 | BASE TABLE |             NULL | NULL               |
| sys                | allocations             | BASE TABLE |             NULL | NULL               |
| sys                | checks                  | BASE TABLE |             NULL | NULL               |
| sys                | cluster                 | BASE TABLE |             NULL | NULL               |
| sys                | health                  | BASE TABLE |             NULL | NULL               |
| sys                | jobs                    | BASE TABLE |             NULL | NULL               |
| sys                | jobs_log                | BASE TABLE |             NULL | NULL               |
| sys                | jobs_metrics            | BASE TABLE |             NULL | NULL               |
| sys                | node_checks             | BASE TABLE |             NULL | NULL               |
| sys                | nodes                   | BASE TABLE |             NULL | NULL               |
| sys                | operations              | BASE TABLE |             NULL | NULL               |
| sys                | operations_log          | BASE TABLE |             NULL | NULL               |
| sys                | privileges              | BASE TABLE |             NULL | NULL               |
| sys                | repositories            | BASE TABLE |             NULL | NULL               |
| sys                | segments                | BASE TABLE |             NULL | NULL               |
| sys                | shards                  | BASE TABLE |             NULL | NULL               |
| sys                | snapshot_restore        | BASE TABLE |             NULL | NULL               |
| sys                | snapshots               | BASE TABLE |             NULL | NULL               |
| sys                | summits                 | BASE TABLE |             NULL | NULL               |
| sys                | users                   | BASE TABLE |             NULL | NULL               |
+--------------------+-------------------------+------------+------------------+--------------------+
SELECT 51 rows in set (... sec)

The table also contains additional information such as the specified routing column and partition columns:

cr> SELECT table_name, clustered_by, partitioned_by
... FROM information_schema.tables
... WHERE table_schema = 'doc'
... ORDER BY table_schema ASC, table_name ASC;
+-------------------+--------------+----------------+
| table_name        | clustered_by | partitioned_by |
+-------------------+--------------+----------------+
| galaxies          | NULL         | NULL           |
| locations         | id           | NULL           |
| partitioned_table | _id          | ["date"]       |
| quotes            | id           | NULL           |
+-------------------+--------------+----------------+
SELECT 4 rows in set (... sec)

Schema

Name

Description

Data Type

blobs_path

The data path of the blob table

TEXT

closed

The state of the table

BOOLEAN

clustered_by

The routing column used to cluster the table

TEXT

column_policy

Defines whether the table uses a STRICT or a DYNAMIC Column policy

TEXT

number_of_replicas

The number of replicas the table currently has

INTEGER

number_of_shards

The number of shards the table is currently distributed across

INTEGER

partitioned_by

The partition columns (used to partition the table)

TEXT

reference_generation

Specifies how values in the self-referencing column are generated

TEXT

routing_hash_function

The name of the hash function used for internal routing

TEXT

self_referencing_column_name

The name of the column that uniquely identifies each row (always _id)

TEXT

settings

WITH

OBJECT

table_catalog

Refers to the table_schema

TEXT

table_name

The name of the table

TEXT

table_schema

The name of the schema the table belongs to

TEXT

table_type

The type of the table (BASE TABLE for tables, VIEW for views)

TEXT

version

A collection of version numbers relevent to the table

OBJECT

settings

Table settings specify configuration parameters for tables. Some settings can be set during Cluster runtime and others are only applied on cluster restart.

This list of table settings in WITH shows detailed information of each parameter.

Table parameters can be applied with CREATE TABLE on creation of a table. With ALTER TABLE they can be set on already existing tables.

The following statement creates a new table and sets the refresh interval of shards to 500 ms and sets the shard allocation for primary shards only:

cr> create table parameterized_table (id integer, content text)
... with ("refresh_interval"=500, "routing.allocation.enable"='primaries');
CREATE OK, 1 row affected (... sec)

The settings can be verified by querying information_schema.tables:

cr> select settings['routing']['allocation']['enable'] as alloc_enable,
...   settings['refresh_interval'] as refresh_interval
... from information_schema.tables
... where table_name='parameterized_table';
+--------------+------------------+
| alloc_enable | refresh_interval |
+--------------+------------------+
| primaries    |              500 |
+--------------+------------------+
SELECT 1 row in set (... sec)

On existing tables this needs to be done with ALTER TABLE statement:

cr> alter table parameterized_table
... set ("routing.allocation.enable"='none');
ALTER OK, -1 rows affected (... sec)

views

The table information_schema.views contains the name, definition and options of all available views.

cr> SELECT table_schema, table_name, view_definition
... FROM information_schema.views
... ORDER BY table_schema ASC, table_name ASC;
+--------------+------------+-------------------------+
| table_schema | table_name | view_definition         |
+--------------+------------+-------------------------+
| doc          | galaxies   | SELECT                  |
|              |            |   "id"                  |
|              |            | , "name"                |
|              |            | , "description"         |
|              |            | FROM "locations"        |
|              |            | WHERE "kind" = 'Galaxy' |
+--------------+------------+-------------------------+
SELECT 1 row in set (... sec)

Schema

Name

Description

Data Type

table_catalog

The catalog of the table of the view (refers to table_schema)

TEXT

table_schema

The schema of the table of the view

TEXT

table_name

The name of the table of the view

TEXT

view_definition

The SELECT statement that defines the view

TEXT

check_option

Not applicable for CrateDB, always return NONE

TEXT

is_updatable

Whether the view is updatable. Not applicable for CrateDB, always returns FALSE

BOOLEAN

owner

The user that created the view

TEXT

Note

If you drop the table of a view, the view will still exist and show up in the information_schema.tables and information_schema.views tables.

columns

This table can be queried to get a list of all available columns of all tables and views and their definition like data type and ordinal position inside the table:

cr> select table_name, column_name, ordinal_position as pos, data_type
... from information_schema.columns
... where table_schema = 'doc' and table_name not like 'my_table%'
... order by table_name asc, column_name asc;
+-------------------+--------------------------------+-----+--------------------------+
| table_name        | column_name                    | pos | data_type                |
+-------------------+--------------------------------+-----+--------------------------+
| locations         | date                           |   3 | timestamp with time zone |
| locations         | description                    |   6 | text                     |
| locations         | id                             |   1 | integer                  |
| locations         | information                    |  11 | object_array             |
| locations         | information['evolution_level'] |  13 | smallint                 |
| locations         | information['population']      |  12 | bigint                   |
| locations         | inhabitants                    |   7 | object                   |
| locations         | inhabitants['description']     |   9 | text                     |
| locations         | inhabitants['interests']       |   8 | text_array               |
| locations         | inhabitants['name']            |  10 | text                     |
| locations         | kind                           |   4 | text                     |
| locations         | landmarks                      |  14 | text_array               |
| locations         | name                           |   2 | text                     |
| locations         | position                       |   5 | integer                  |
| partitioned_table | date                           |   3 | timestamp with time zone |
| partitioned_table | id                             |   1 | bigint                   |
| partitioned_table | title                          |   2 | text                     |
| quotes            | id                             |   1 | integer                  |
| quotes            | quote                          |   2 | text                     |
+-------------------+--------------------------------+-----+--------------------------+
SELECT 19 rows in set (... sec)

You can even query this table’s own columns (attention: this might lead to infinite recursion of your mind, beware!):

cr> select column_name, data_type, ordinal_position
... from information_schema.columns
... where table_schema = 'information_schema'
... and table_name = 'columns' order by column_name asc;
+--------------------------+-----------+------------------+
| column_name              | data_type | ordinal_position |
+--------------------------+-----------+------------------+
| character_maximum_length | integer   |                1 |
| character_octet_length   | integer   |                2 |
| character_set_catalog    | text      |                3 |
| character_set_name       | text      |                4 |
| character_set_schema     | text      |                5 |
| check_action             | integer   |                6 |
| check_references         | text      |                7 |
| collation_catalog        | text      |                8 |
| collation_name           | text      |                9 |
| collation_schema         | text      |               10 |
| column_default           | text      |               11 |
| column_name              | text      |               12 |
| data_type                | text      |               13 |
| datetime_precision       | integer   |               14 |
| domain_catalog           | text      |               15 |
| domain_name              | text      |               16 |
| domain_schema            | text      |               17 |
| generation_expression    | text      |               18 |
| interval_precision       | integer   |               19 |
| interval_type            | text      |               20 |
| is_generated             | text      |               21 |
| is_nullable              | boolean   |               22 |
| numeric_precision        | integer   |               23 |
| numeric_precision_radix  | integer   |               24 |
| numeric_scale            | integer   |               25 |
| ordinal_position         | integer   |               26 |
| table_catalog            | text      |               27 |
| table_name               | text      |               28 |
| table_schema             | text      |               29 |
| udt_catalog              | text      |               30 |
| udt_name                 | text      |               31 |
| udt_schema               | text      |               32 |
+--------------------------+-----------+------------------+
SELECT 32 rows in set (... sec)

Schema

Name

Description

Data Type

table_catalog

Refers to the table_schema

TEXT

table_schema

Schema name containing the table

TEXT

table_name

Table Name

TEXT

column_name

Column Name For fields in object columns this is not an identifier but a path and therefore must not be double quoted when programmatically obtained.

TEXT

ordinal_position

The position of the column within the table

INTEGER

is_nullable

Whether the column is nullable

BOOLEAN

data_type

The data type of the column

For further information see Data types

TEXT

column_default

The default expression of the column

TEXT

character_maximum_length

If the data type is a character type then return the declared length limit; otherwise NULL.

INTEGER

character_octet_length

Not implemented (always returns NULL)

Please refer to text type

INTEGER

numeric_precision

Indicates the number of significant digits for a numeric data_type. For all other data types this column is NULL.

INTEGER

numeric_precision_radix

Indicates in which base the value in the column numeric_precision for a numeric data_type is exposed. This can either be 2 (binary) or 10 (decimal). For all other data types this column is NULL.

INTEGER

numeric_scale

Not implemented (always returns NULL)

INTEGER

datetime_precision

Contains the fractional seconds precision for a timestamp data_type. For all other data types this column is null.

INTEGER

interval_type

Not implemented (always returns NULL)

TEXT

interval_precision

Not implemented (always returns NULL)

INTEGER

character_set_catalog

Not implemented (always returns NULL)

TEXT

character_set_schema

Not implemented (always returns NULL)

TEXT

character_set_name

Not implemented (always returns NULL)

TEXT

collation_catalog

Not implemented (always returns NULL)

TEXT

collation_schema

Not implemented (always returns NULL)

TEXT

collation_name

Not implemented (always returns NULL)

TEXT

domain_catalog

Not implemented (always returns NULL)

TEXT

domain_schema

Not implemented (always returns NULL)

TEXT

domain_name

Not implemented (always returns NULL)

TEXT

udt_catalog

Not implemented (always returns NULL)

TEXT

udt_schema

Not implemented (always returns NULL)

TEXT

udt_name

Not implemented (always returns NULL)

TEXT

check_references

Not implemented (always returns NULL)

TEXT

check_action

Not implemented (always returns NULL)

INTEGER

generation_expression

The expression used to generate ad column. If the column is not generated NULL is returned.

TEXT

is_generated

Returns ALWAYS or NEVER wether the column is generated or not.

TEXT

table_constraints

This table can be queried to get a list of all defined table constraints, their type, name and which table they are defined in.

Note

Currently only PRIMARY_KEY constraints are supported.

cr> select table_schema, table_name, constraint_name, constraint_type as type
... from information_schema.table_constraints
... where table_name = 'tables'
...   or table_name = 'quotes'
...   or table_name = 'documents'
...   or table_name = 'tbl'
... order by table_schema desc, table_name asc limit 10;
+--------------------+------------+-...------------------+-------------+
| table_schema       | table_name | constraint_name      | type        |
+--------------------+------------+-...------------------+-------------+
| information_schema | tables     | tables_pk            | PRIMARY KEY |
| doc                | quotes     | quotes_pk            | PRIMARY KEY |
| doc                | tbl        | doc_tbl_col_not_null | CHECK       |
+--------------------+------------+-...------------------+-------------+
SELECT 3 rows in set (... sec)

key_column_usage

This table may be queried to retrieve primary key information from all user tables:

cr> select constraint_name, table_name, column_name, ordinal_position
... from information_schema.key_column_usage
... where table_name = 'students'
+-----------------+------------+-------------+------------------+
| constraint_name | table_name | column_name | ordinal_position |
+-----------------+------------+-------------+------------------+
| students_pk     | students   | id          |                1 |
| students_pk     | students   | department  |                2 |
+-----------------+------------+-------------+------------------+
SELECT 2 rows in set (... sec)

Schema

Name

Description

Data Type

constraint_catalog

Refers to table_catalog

TEXT

constraint_schema

Refers to table_schema

TEXT

constraint_name

Name of the constraint

TEXT

table_catalog

Refers to table_schema

TEXT

table_schema

Name of the schema that contains the table that contains the constraint

TEXT

table_name

Name of the table that contains the constraint

TEXT

column_name

Name of the column that contains the constraint

TEXT

ordinal_position

Position of the column within the contraint (starts with 1)

INTEGER

table_partitions

This table can be queried to get information about all partitioned tables, Each partition of a table is represented as one row. The row contains the information table name, schema name, partition ident, and the values of the partition. values is a key-value object with the partition column (or columns) as key(s) and the corresponding value as value(s).

cr> insert into a_partitioned_table (id, content) values (1, 'content_a');
INSERT OK, 1 row affected (... sec)
cr> alter table a_partitioned_table set (number_of_shards=5);
ALTER OK, -1 rows affected (... sec)
cr> insert into a_partitioned_table (id, content) values (2, 'content_b');
INSERT OK, 1 row affected (... sec)

The following example shows a table where the column content of table a_partitioned_table has been used to partition the table. The table has two partitions. The partitions are introduced when data is inserted where content is content_a, and content_b.:

cr> select table_name, table_schema as schema, partition_ident, "values"
... from information_schema.table_partitions
... order by table_name, partition_ident;
+---------------------+--------+--------------------+--------------------------+
| table_name          | schema | partition_ident    | values                   |
+---------------------+--------+--------------------+--------------------------+
| a_partitioned_table | doc    | 04566rreehimst2vc4 | {"content": "content_a"} |
| a_partitioned_table | doc    | 04566rreehimst2vc8 | {"content": "content_b"} |
+---------------------+--------+--------------------+--------------------------+
SELECT 2 rows in set (... sec)

The second partition has been created after the number of shards for future partitions have been changed on the partitioned table, so they show 5 instead of 4:

cr> select table_name, partition_ident,
... number_of_shards, number_of_replicas
... from information_schema.table_partitions
... order by table_name, partition_ident;
+---------------------+--------------------+------------------+--------------------+
| table_name          | partition_ident    | number_of_shards | number_of_replicas |
+---------------------+--------------------+------------------+--------------------+
| a_partitioned_table | 04566rreehimst2vc4 |                4 | 0-1                |
| a_partitioned_table | 04566rreehimst2vc8 |                5 | 0-1                |
+---------------------+--------------------+------------------+--------------------+
SELECT 2 rows in set (... sec)

routines

The routines table contains tokenizers, token-filters, char-filters, custom analyzers created by CREATE ANALYZER statements (see Creating a custom analyzer), and functions created by CREATE FUNCTION statements:

cr> select routine_name, routine_type
... from information_schema.routines
... group by routine_name, routine_type
... order by routine_name asc limit 5;
+----------------------+--------------+
| routine_name         | routine_type |
+----------------------+--------------+
| PathHierarchy        | TOKENIZER    |
| apostrophe           | TOKEN_FILTER |
| arabic               | ANALYZER     |
| arabic_normalization | TOKEN_FILTER |
| arabic_stem          | TOKEN_FILTER |
+----------------------+--------------+
SELECT 5 rows in set (... sec)

For example you can use this table to list existing tokenizers like this:

cr> select routine_name
... from information_schema.routines
... where routine_type='TOKENIZER'
... order by routine_name asc limit 10;
+----------------+
| routine_name   |
+----------------+
| PathHierarchy  |
| char_group     |
| classic        |
| edge_ngram     |
| keyword        |
| letter         |
| lowercase      |
| ngram          |
| path_hierarchy |
| pattern        |
+----------------+
SELECT 10 rows in set (... sec)

Or get an overview of how many routines and routine types are available:

cr> select count(*), routine_type
... from information_schema.routines
... group by routine_type
... order by routine_type;
+----------+--------------+
| count(*) | routine_type |
+----------+--------------+
|       45 | ANALYZER     |
|        3 | CHAR_FILTER  |
|       16 | TOKENIZER    |
|       62 | TOKEN_FILTER |
+----------+--------------+
SELECT 4 rows in set (... sec)

Schema

Name

Data Type

routine_name

TEXT

routine_type

TEXT

routine_body

TEXT

routine_schema

TEXT

data_type

TEXT

is_deterministic

BOOLEAN

routine_definition

TEXT

specific_name

TEXT

routine_name

Name of the routine (might be duplicated in case of overloading)

routine_type

Type of the routine. Can be FUNCTION, ANALYZER, CHAR_FILTER, TOKEN_FILTER or TOKEN_FILTER.

routine_schema

The schema where the routine was defined. If it doesn’t apply, then NULL.

routine_body

The language used for the routine implementation. If it doesn’t apply, then NULL.

data_type

The return type of the function. If it doesn’t apply, then NULL.

is_deterministic

If the routine is deterministic then True, else False (NULL if it doesn’t apply).

routine_definition

The function definition (NULL if it doesn’t apply).

specific_name

Used to uniquely identify the function in a schema, even if the function is overloaded. Currently the specific name contains the types of the function arguments. As the format might change in the future, it should be only used to compare it to other instances of specific_name.

schemata

The schemata table lists all existing schemas. Thes blob, information_schema, and sys schemas are always available. The doc schema is available after the first user table is created.

cr> select schema_name from information_schema.schemata order by schema_name;
+--------------------+
| schema_name        |
+--------------------+
| blob               |
| doc                |
| information_schema |
| pg_catalog         |
| sys                |
+--------------------+
SELECT 5 rows in set (... sec)

sql_features

The sql_features table outlines supported and unsupported SQL features of CrateDB based to the current SQL standard (see SQL standard compliance):

cr> select feature_name, is_supported, sub_feature_id, sub_feature_name
... from information_schema.sql_features
... where feature_id='F501';
+--------------------------------+--------------+----------------+--------------------+
| feature_name                   | is_supported | sub_feature_id | sub_feature_name   |
+--------------------------------+--------------+----------------+--------------------+
| Features and conformance views | FALSE        |                |                    |
| Features and conformance views | TRUE         | 1              | SQL_FEATURES view  |
| Features and conformance views | FALSE        | 2              | SQL_SIZING view    |
| Features and conformance views | FALSE        | 3              | SQL_LANGUAGES view |
+--------------------------------+--------------+----------------+--------------------+
SELECT 4 rows in set (... sec)

Name

Data Type

Nullable

feature_id

TEXT

NO

feature_name

TEXT

NO

sub_feature_id

TEXT

NO

sub_feature_name

TEXT

NO

is_supported

TEXT

NO

is_verified_by

TEXT

YES

comments

TEXT

YES

feature_id

Identifier of the feature

feature_name

Descriptive name of the feature by the Standard

sub_feature_id

Identifier of the subfeature; If it has zero-length, this is a feature

sub_feature_name

Descriptive name of the subfeature by the Standard; If it has zero-length, this is a feature

is_supported

YES if the feature is fully supported by the current version of CrateDB, NO if not

is_verified_by

Identifies the conformance test used to verify the claim;

Always NULL since the CrateDB development group does not perform formal testing of feature conformance

comments

Either NULL or shows a comment about the supported status of the feature

character_sets

The character_sets table identifies the character sets available in the current database.

In CrateDB there is always a single entry listing UTF8:

cr> SELECT character_set_name, character_repertoire FROM information_schema.character_sets;
+--------------------+----------------------+
| character_set_name | character_repertoire |
+--------------------+----------------------+
| UTF8               | UCS                  |
+--------------------+----------------------+
SELECT 1 row in set (... sec)

Column Name

Return Type

Description

character_set_catalog

TEXT

Not implemented, this column is always null.

character_set_schema

TEXT

Not implemented, this column is always null.

character_set_name

TEXT

Name of the character set

character_repertoire

TEXT

Character repertoire

form_of_use

TEXT

Character encoding form, same as character_set_name

default_collate_catalog

TEXT

Name of the database containing the default collation (Always crate)

default_collate_schema

TEXT

Name of the schema containing the default collation (Always NULL)

default_collate_name

TEXT

Name of the default collation (Always NULL)

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