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: The functions of shobj_description and obj_description are similar. The only difference is that shobj_description is used for 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.