Comment Checking Functions

col_description(table_oid, column_number)

Description: Gets comment for a table column.

Return type: text

Note: col_description returns the comment for a table column, which is specified by the OID of its table and its column number.

Example: Query the pg_class system catalog to obtain the table OID, and query the INFORMATION_SCHEMA.COLUMNS system view to obtain column_number.

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SELECT COLUMN_NAME,ORDINAL_POSITION FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 't' AND COLUMN_NAME = 'a';
column_name | ordinal_position
-------------+------------------
a           |                1
(1 row)

SELECT oid FROM pg_class WHERE relname='t';
  oid
-------
 44020
(1 row)

SELECT col_description(44020,1);
    col_description
-----------------------
 This is a test table.
(1 row)

obj_description(object_oid, catalog_name)

Description: Gets comment for a database object.

Return type: text

Note: The two-parameter form of obj_description returns the comment for a database object specified by its OID and the name of the containing system catalog. For example, obj_description(123456,'pg_class') would retrieve the comment for the table with OID 123456. The one-parameter form of obj_description requires only the object OID.

obj_description cannot be used for table columns since columns do not have OIDs of their own.

obj_description(object_oid)

Description: Gets comment for a database object.

Return type: text

shobj_description(object_oid, catalog_name)

Description: Gets comment for a shared database object.

Return type: text

Note: shobj_description is used just like obj_description except the former is used for retrieving comments on shared objects. Some system catalogs are global to all databases within each cluster, and the comments for objects in them are stored globally as well.