doc: mention unusability of dropped CHECK to verify NOT NULL It's possible to use a CHECK (col IS NOT NULL) constraint to skip scanning a table for nulls when adding a NOT NULL constraint on the same column. However, if the CHECK constraint is dropped on the same command that the NOT NULL is added, this fails, i.e., makes the NOT NULL addition slow. The best we can do about it at this stage is to document this so that users aren't taken by surprise.
(In Postgres 18 you can directly add the NOT NULL constraint as NOT VALID instead, so there's no longer much use for the CHECK constraint, therefore no point in building mechanism to support the case better.) Reported-by: Andrew <psy2000...@yahoo.com> Reviewed-by: David G. Johnston <david.g.johns...@gmail.com> Discussion: https://postgr.es/m/175385113607.786.16774570234342968...@wrigleys.postgresql.org Branch ------ REL_18_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/7b1053a577494871acb5e91c63abb2bade5b8dea Modified Files -------------- doc/src/sgml/ref/alter_table.sgml | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
