From 4c2c602381dac1db2d20874e4b9c8320ed4aa5af Mon Sep 17 00:00:00 2001 From: "Chao Li (Evan)" Date: Thu, 26 Feb 2026 13:43:24 +0800 Subject: [PATCH v3] doc: Clarify that empty COMMENT string removes the comment Clarify the documentation of COMMENT ON to state that specifying an empty string is treated as NULL, meaning that the comment is removed. This makes the behavior explicit and avoids possible confusion about how empty strings are handled. Also adds a regress test case that uses empty string to remove a comment. Author: Chao Li Reviewed-by: Fujii Masao Reviewed-by: Ashutosh Bapat Reviewed-by: David G. Johnston Reviewed-by: Shengbin Zhao Reviewed-by: Jim Jones Discussion: https://postgr.es/m/26476097-B1C1-4BA8-AA92-0AD0B8EC7190@gmail.com --- doc/src/sgml/ref/comment.sgml | 18 +++++++++++------- src/test/regress/expected/create_index.out | 14 ++++++++++++++ src/test/regress/sql/create_index.sql | 4 ++++ 3 files changed, 29 insertions(+), 7 deletions(-) diff --git a/doc/src/sgml/ref/comment.sgml b/doc/src/sgml/ref/comment.sgml index 8d81244910b..fa71144c914 100644 --- a/doc/src/sgml/ref/comment.sgml +++ b/doc/src/sgml/ref/comment.sgml @@ -80,14 +80,16 @@ COMMENT ON Description - COMMENT stores a comment about a database object. + COMMENT stores, replaces, or removes the comment on a + database object. - Only one comment string is stored for each object, so to modify a comment, - issue a new COMMENT command for the same object. To remove a - comment, write NULL in place of the text string. - Comments are automatically dropped when their object is dropped. + Only one comment string is stored for each object. Issuing a new + COMMENT command for the same object replaces the + existing comment. Specifying NULL or an empty + string ('') removes the comment. Comments are + automatically dropped when their object is dropped. @@ -266,7 +268,8 @@ COMMENT ON string_literal - The new comment contents, written as a string literal. + The new comment contents, written as a string literal. An empty string + ('') removes the comment. @@ -275,7 +278,7 @@ COMMENT ON NULL - Write NULL to drop the comment. + Write NULL to remove the comment. @@ -362,6 +365,7 @@ COMMENT ON TRANSFORM FOR hstore LANGUAGE plpython3u IS 'Transform between hstore COMMENT ON TRIGGER my_trigger ON my_table IS 'Used for RI'; COMMENT ON TYPE complex IS 'Complex number data type'; COMMENT ON VIEW my_view IS 'View of departmental costs'; +COMMENT ON VIEW my_view IS NULL; diff --git a/src/test/regress/expected/create_index.out b/src/test/regress/expected/create_index.out index c743fc769cb..55538c4c41e 100644 --- a/src/test/regress/expected/create_index.out +++ b/src/test/regress/expected/create_index.out @@ -32,6 +32,20 @@ COMMENT ON INDEX six_wrong IS 'bad index'; ERROR: relation "six_wrong" does not exist COMMENT ON INDEX six IS 'good index'; COMMENT ON INDEX six IS NULL; +SELECT obj_description('six'::regclass, 'pg_class') IS NULL AS six_comment_is_null; + six_comment_is_null +--------------------- + t +(1 row) + +COMMENT ON INDEX six IS 'add the comment back'; +COMMENT ON INDEX six IS ''; -- empty string removes the comment, same as NULL +SELECT obj_description('six'::regclass, 'pg_class') IS NULL AS six_comment_is_null; + six_comment_is_null +--------------------- + t +(1 row) + -- -- BTREE partial indices -- diff --git a/src/test/regress/sql/create_index.sql b/src/test/regress/sql/create_index.sql index eabc9623b20..82e4062a215 100644 --- a/src/test/regress/sql/create_index.sql +++ b/src/test/regress/sql/create_index.sql @@ -45,6 +45,10 @@ CREATE INDEX six ON shighway USING btree (name text_ops); COMMENT ON INDEX six_wrong IS 'bad index'; COMMENT ON INDEX six IS 'good index'; COMMENT ON INDEX six IS NULL; +SELECT obj_description('six'::regclass, 'pg_class') IS NULL AS six_comment_is_null; +COMMENT ON INDEX six IS 'add the comment back'; +COMMENT ON INDEX six IS ''; -- empty string removes the comment, same as NULL +SELECT obj_description('six'::regclass, 'pg_class') IS NULL AS six_comment_is_null; -- -- BTREE partial indices -- 2.50.1 (Apple Git-155)