How to Add / Remove comments to a table or column using the COMMENT ON statement.

In Oracle, you can add comments to a table or column using the COMMENT ON statement.

1. Adding a Comment to a Table

COMMENT ON TABLE table_name IS 'Your table description';

Example:

COMMENT ON TABLE employees IS 'Stores employee details including personal and job-related information';

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2. Adding a Comment to a Column

COMMENT ON COLUMN table_name.column_name IS 'Your column description';

Example:

COMMENT ON COLUMN employees.salary IS 'Salary of the employee in USD';

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3. Viewing Comments

To check table and column comments, query the data dictionary views:

• For table comments:

  SELECT table_name, comments 
  FROM user_tab_comments 
  WHERE table_name = 'EMPLOYEES';
  

• For column comments:

  SELECT column_name, comments 
  FROM user_col_comments 
  WHERE table_name = 'EMPLOYEES';
  

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4. Removing Comments

To remove a comment, set it to NULL:

COMMENT ON TABLE employees IS NULL;
COMMENT ON COLUMN employees.salary IS NULL;