Shulou(Shulou.com)06/01 Report--

Alter table Salter column SN CHAR (8) not NULL-- set the SN to non-empty (but there is no name of the named constraint here, how can I delete it? ) alter table Salter column SN CHAR (8) NULL-sets SN to allow null values (guess a non-null constraint has been removed, but how does it correspond to that constraint name? ) alter table Sadd constraint SN_Cons check (SN is not null)-- create a self-named constraint (check and is are omitted here and an error is reported) alter table sdrop constraint SN_Cons-- deletes the constraint with the specified name

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