Lesson 35 - COMMENT statement

COMMENT statement is used to add a comment(description) about a table, view, materialized view, or column into the data dictionary.

Syntax for Table level comment:

COMMENT ON <table name > IS 'string' ;

Example :

SQL> comment on employee is ' This table is for holding employee details' ;

SQL> comment on dept is ' This table is created by Russwelt on 01-Dec-2012';

Syntax for column level comment :

COMMENT ON <tablename.column name > IS 'string' ;

Column level comments are to add description about column

Examples :

SQL> comment on emp.hiredate is 'This is to store joining date of employee';

SQL> comment on emp.mgr is 'This is to store manager name of the employee';

We can view the comments on a particular table or column by querying the following data dictionary views.

USER_TAB_COMMENTS - For table level comments

USER_COL_COMMENTS - For column level comments

To drop comments :

We have to give empty string to remove existing commnets in tables or columns

Examples :

SQL> comment on employee is '';

SQL> comment on emp.hiredate is '';