Materialize/doc/user/content/sql/comment-on.md

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title: "COMMENT ON" description: "COMMENT ON ... adds or updates the comment of an object." menu: main:

parent: 'commands'

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COMMENT ON ... adds or updates the comment of an object.

Syntax

{{< diagram "comment-on.svg" >}}

Details

COMMENT ON stores a comment about an object in the database. Each object can only have one comment associated with it, so successive calls of COMMENT ON to a single object will overwrite the previous comment.

To read the comment on an object you need to query the mz_internal.mz_comments catalog table.

Privileges

The privileges required to execute this statement are:

{{< include-md file="shared-content/sql-command-privileges/comment-on.md" >}}

For more information on ownership and privileges, see Role-based access control.

Examples

--- Add comments.
COMMENT ON TABLE foo IS 'this table is important';
COMMENT ON COLUMN foo.x IS 'holds all of the important data';

--- Update a comment.
COMMENT ON TABLE foo IS 'holds non-important data';

--- Remove a comment.
COMMENT ON TABLE foo IS NULL;

--- Read comments.
SELECT * FROM mz_internal.mz_comments;