System Catalog Information Functions

format_type(type_oid, typemod)

Description: Gets SQL name of a data type.

Return type: text

Note:

format_type returns the SQL name of a data type that is identified by its type OID and possibly a type modifier. Pass NULL for the type modifier if no specific modifier is known. Certain type modifiers are passed for data types with length limitations. The SQL name returned from format_type contains the length of the data type, which can be calculated by taking sizeof(int32) from actual storage length [actual storage len - sizeof(int32)] in the unit of bytes. 32-bit space is required to store the customized length set by users. So the actual storage length contains 4 bytes more than the customized length. In the following example, the SQL name returned from format_type is character varying(6), indicating the length of varchar type is 6 bytes. So the actual storage length of varchar type is 10 bytes.

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SELECT format_type((SELECT oid FROM pg_type WHERE typname='varchar'), 10);
     format_type      
----------------------
 character varying(6)
(1 row)

pg_check_authid(role_oid)

Description: Check whether a role name with given OID exists.

Return type: Boolean

pg_describe_object(catalog_id, object_id, object_sub_id)

Description: Gets description of a database object.

Return type: text

Note: pg_describe_object returns a description of a database object specified by catalog OID, object OID and a (possibly zero) sub-object ID. This is useful to determine the identity of an object as stored in the pg_depend catalog.

pg_get_constraintdef(constraint_oid)

Description: Gets definition of a constraint.

Return type: text

pg_get_constraintdef(constraint_oid, pretty_bool)

Description: Gets definition of a constraint.

Return type: text

Note: pg_get_constraintdef and pg_get_indexdef respectively reconstruct the creating command for a constraint and an index.

pg_get_expr(pg_node_tree, relation_oid)

Description: Decompiles internal form of an expression, assuming that any Vars in it refer to the relationship indicated by the second parameter.

Return type: text

pg_get_expr(pg_node_tree, relation_oid, pretty_bool)

Description: Decompiles internal form of an expression, assuming that any Vars in it refer to the relationship indicated by the second parameter.

Return type: text

Note: pg_get_expr decompiles the internal form of an individual expression, such as the default value for a column. It can be useful when examining the contents of system catalogs. If the expression might contain Vars, specify the OID of the relationship they refer to as the second parameter; if no Vars are expected, zero is sufficient.

pg_get_functiondef(func_oid)

Description: Gets definition of a function.

Return type: text

func_oid is the OID of the function, which can be queried in the PG_PROC system catalog.

Example: Query the OID and definition of the justify_days function.

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SELECT oid FROM pg_proc WHERE proname ='justify_days';
 oid
------
 1295
(1 row)

SELECT * FROM pg_get_functiondef(1295);
 headerlines |                          definition
-------------+--------------------------------------------------------------
           4 | CREATE OR REPLACE FUNCTION pg_catalog.justify_days(interval)+
             |  RETURNS interval                                           +
             |  LANGUAGE internal                                          +
             |  IMMUTABLE STRICT NOT FENCED NOT SHIPPABLE                  +
             | AS $function$interval_justify_days$function$                +
             |
(1 row)

pg_get_function_arguments(func_oid)

Description: Gets argument list of function's definition (with default values).

Return type: text

Note: pg_get_function_arguments returns the argument list of a function, in the form it would need to appear in within CREATE FUNCTION.

pg_get_function_identity_arguments(func_oid)

Description: Gets argument list to identify a function (without default values).

Return type: text

Note: pg_get_function_identity_arguments returns the argument list necessary to identify a function, in the form it would need to appear in within ALTER FUNCTION. This form omits default values.

pg_get_function_result(func_oid)

Description: Gets RETURNS clause for function.

Return type: text

Note: pg_get_function_result returns the appropriate RETURNS clause for the function.

pg_get_indexdef(index_oid)

Description: Gets CREATE INDEX command for index.

Return type: text

index_oid indicates the index OID, which can be queried in the PG_STATIO_ALL_INDEXES system view.

Example: Query the OID and CREATE INDEX command of index ds_ship_mode_t1_index1.

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SELECT indexrelid FROM PG_STATIO_ALL_INDEXES WHERE indexrelname = 'ds_ship_mode_t1_index1';
 indexrelid
------------
     136035
(1 row)
SELECT * FROM pg_get_indexdef(136035);
                                                pg_get_indexdef
---------------------------------------------------------------------------------------------------------------
 CREATE INDEX ds_ship_mode_t1_index1 ON tpcds.ship_mode_t1 USING psort (sm_ship_mode_sk) TABLESPACE pg_default
(1 row)

pg_get_indexdef(index_oid, column_no, pretty_bool)

Description: Gets CREATE INDEX command for index, or definition of just one index column when column_no is not zero.

Return type: text

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SELECT * FROM pg_get_indexdef(136035,0,false);
                                                pg_get_indexdef
---------------------------------------------------------------------------------------------------------------
 CREATE INDEX ds_ship_mode_t1_index1 ON tpcds.ship_mode_t1 USING psort (sm_ship_mode_sk) TABLESPACE pg_default
(1 row)
SELECT * FROM pg_get_indexdef(136035,1,false);
 pg_get_indexdef
-----------------
 sm_ship_mode_sk
(1 row)

pg_get_keywords()

Description: Gets list of SQL keywords and their categories.

Return type: SETOF record

Note: pg_get_keywords returns a set of records describing the SQL keywords recognized by the server. The word column contains the keyword. The catcode column contains a category code: U for unreserved, C for column name, T for type or function name, or R for reserved. The catdesc column contains a possibly-localized string describing the category.

pg_get_ruledef(rule_oid)

Description: Gets CREATE RULE command for a rule.

Return type: text

pg_get_ruledef(rule_oid, pretty_bool)

Description: Gets CREATE RULE command for a rule.

Return type: text

pg_get_userbyid(role_oid)

Description: Gets role name with given OID.

Return type: name

Note: pg_get_userbyid extracts a role's name given its OID.

pg_get_viewdef(viewname text [, pretty bool [, fullflag bool]])

Description: gets underlying SELECT command for views.

Return type: text

Note:

• pg_get_viewdef reconstructs the SELECT query that defines a view. If the value of pretty bool is set to true, the display format is suitable for printing and more readable. The default value of pretty bool is false, and the display format is not readable. Use the default format for dump purposes whenever possible. The pretty bool parameter can be applied only to valid views.
• When fullflag bool is set to true, the complete definition of the view is displayed. The default value is false.

pg_get_viewdef(viewoid oid [, pretty bool [, fullflag bool]])

Description: gets underlying SELECT command for views.

Return type: text

pg_get_viewdef(view_oid, wrap_column_int)

Description: Gets underlying SELECT command for view, wrapping lines with columns as specified, printing is implied.

Return type: text

pg_get_tabledef(table_oid)

Description: Obtains a table definition based on table_oid.

Return type: text

Example: Obtain the OID of the table customer_t2 from the system catalog pg_class, and then use this function to query the definition of customer_t2 to obtain the table columns, storage mode (row-store or column-store), and table distribution mode configured for customer_t2 when it is created.

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select oid from pg_class where relname ='customer_t2';
  oid
-------
 17353
(1 row)

select * from pg_get_tabledef(17353);
              pg_get_tabledef
--------------------------------------------
 SET search_path = dbadmin;                +
 CREATE  TABLE customer_t2 (               +
         state_id character(2),            +
         state_name character varying(40), +
         area_id numeric                   +
 )                                         +
 WITH (orientation=column, compression=low)+
 DISTRIBUTE BY HASH(state_id)              +
 TO GROUP group_version1;
(1 row)

pg_get_tabledef(table_name)

Description: Obtains a table definition based on table_name.

Return type: text

Remarks: pg_get_tabledef reconstructs the CREATE statement of the table definition, including the table definition, index information, and comments. Users need to create the dependent objects of the table, such as groups, schemas, tablespaces, and servers. The table definition does not include the statements for creating these dependent objects.

pg_options_to_table(reloptions)

Description: Gets the set of storage option name/value pairs.

Return type: SETOF record

Note: pg_options_to_table returns the set of storage option name/value pairs (option_name/option_value) when passing pg_class.reloptions or pg_attribute.attoptions.

pg_typeof(any)

Description: Gets the data type of any value.

Return type: regtype

Note:

pg_typeof returns the OID of the data type of the value that is passed to it. This can be helpful for troubleshooting or dynamically constructing SQL queries. The function is declared as returning regtype, which is an OID alias type (see Object Identifier Types). This means that it is the same as an OID for comparison purposes but displays as a type name.

Example:

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SELECT pg_typeof(33);
 pg_typeof 
-----------
 integer
(1 row)

SELECT typlen FROM pg_type WHERE oid = pg_typeof(33);
 typlen 
--------
      4
(1 row)

collation for (any)

Description: Gets the collation of the parameter.

Return type: text

Note:

The expression collation for returns the collation of the value that is passed to it. Example:

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SELECT collation for (description) FROM pg_description LIMIT 1;
 pg_collation_for 
------------------
 "default"
(1 row)

The value might be quoted and schema-qualified. If no collation is derived for the argument expression, then a null value is returned. If the parameter is not of a collectable data type, then an error is thrown.

getdistributekey(table_name)

Description: Gets a distribution column for a hash table.

Return type: text

Example:

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SELECT getdistributekey('item');
 getdistributekey 
------------------
 i_item_sk
(1 row)