From a99a5a8a883625dd297958dcd6649696aa2887fb Mon Sep 17 00:00:00 2001 From: "Chao Li (Evan)" Date: Fri, 29 May 2026 06:47:07 +0800 Subject: [PATCH v8 2/3] doc: Clarify inherited constraint behavior Update the table inheritance documentation to mention not-null constraints alongside check constraints where inherited constraints are discussed. Also clarify that some properties of inherited constraints can now be altered directly on child tables, while the resulting constraint must remain compatible with its inherited parent constraints. For multiple inheritance, say explicitly that when a column or constraint is inherited from more than one parent, the stricter definition applies. Author: Chao Li Reviewed-by: Zsolt Parragi Discussion: https://postgr.es/m/E74C57FA-1DD0-4C8E-8FB1-538034752592@gmail.com --- doc/src/sgml/ddl.sgml | 33 +++++++++++++++++++-------------- 1 file changed, 19 insertions(+), 14 deletions(-) diff --git a/doc/src/sgml/ddl.sgml b/doc/src/sgml/ddl.sgml index 747f929aee3..dac31457267 100644 --- a/doc/src/sgml/ddl.sgml +++ b/doc/src/sgml/ddl.sgml @@ -4090,7 +4090,9 @@ VALUES ('Albany', NULL, NULL, 'NY'); similar fashion. Thus, for example, a merged column will be marked not-null if any one of the column definitions it came from is marked not-null. Check constraints are merged if they have the same name, - and the merge will fail if their conditions are different. + and the merge will fail if their conditions are different. For merged + check constraints, stricter enforceability is preserved: if any inherited + copy is enforced, the merged constraint is enforced. @@ -4104,8 +4106,9 @@ VALUES ('Albany', NULL, NULL, 'NY'); To do this the new child table must already include columns with the same names and types as the columns of the parent. It must also include check constraints with the same names and check expressions as those of the - parent. Similarly an inheritance link can be removed from a child using the - NO INHERIT variant of ALTER TABLE. + parent, as well as matching not-null constraints. Similarly an inheritance + link can be removed from a child using the NO INHERIT + variant of ALTER TABLE. Dynamically adding and removing inheritance links like this can be useful when the inheritance relationship is being used for table partitioning (see ). @@ -4124,21 +4127,23 @@ VALUES ('Albany', NULL, NULL, 'NY'); A parent table cannot be dropped while any of its children remain. Neither - can columns or check constraints of child tables be dropped or altered - if they are inherited - from any parent tables. If you wish to remove a table and all of its - descendants, one easy way is to drop the parent table with the - CASCADE option (see ). + can inherited columns or inherited check and not-null constraints of child + tables be dropped directly. Some properties of inherited constraints can + be altered, but each resulting constraint must remain compatible with all + parent constraints from which it is inherited. If you wish to remove a + table and all of its descendants, one easy way is to drop the parent table + with the CASCADE option (see ). ALTER TABLE will - propagate any changes in column data definitions and check - constraints down the inheritance hierarchy. Again, dropping - columns that are depended on by other tables is only possible when using - the CASCADE option. ALTER - TABLE follows the same rules for duplicate column merging - and rejection that apply during CREATE TABLE. + propagate changes in column definitions and in inheritable constraints + (check and not-null constraints) down the inheritance hierarchy. Again, + dropping columns that are depended on by other tables is only possible + when using the CASCADE option. ALTER + TABLE follows the same rules for merging or rejecting duplicate + inherited column and constraint definitions that apply during + CREATE TABLE. -- 2.50.1 (Apple Git-155)