patternsqlModerate
Is there anything a table-level constraint declaration can do that a column-level one can not do?
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Problem
Had an exam today. One question disturbed me:
What can a table-level constraint do that a column-level constraint can't do?
My answer was that only a table-level constraint declaration permits setting up a composite primary key. I guess this is not the only difference. How could I have added to that?
What can a table-level constraint do that a column-level constraint can't do?
My answer was that only a table-level constraint declaration permits setting up a composite primary key. I guess this is not the only difference. How could I have added to that?
Solution
You've forgotten about other types of constraint than primary key (also applies to unique, check, and foreign key constraints) but that's basically it.
A column-level constraint can only reference the column that it is declared next to. A table-level constraint can reference multiple columns.
A column-level constraint can only reference the column that it is declared next to. A table-level constraint can reference multiple columns.
Context
StackExchange Database Administrators Q#50885, answer score: 14
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