difference between table level constraint and column level and
advantages of table level constraint
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Answer Posted / santosh kumar
Let me explain both sides of the coin bit more clearly.
Table level Constraint
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1. Constraints are defined separately after the columns are defined.
2. While defining constraints at this level constraint name must be provided
3. Not null constraints can't be defined at this level.
4. Composite keys can be defined at this level only.
A table level constraint can see every column in the table.
Column level Constraint
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1. Constraints are defined along with the columns.
2. So constraint name is not required.
3. Not null constraints can be defined at this level only(NOT NULL constraint can only apply to one column).
4. Composite keys can't be defined at this level .
5. Column level constraint is more clear syntactically and more meaningful.
A column level constraint has scope only to the column it is defined on.
The major difference between the two constraint is the scope. So far as the use of constraints (validating proper data) is concerned they are pretty much the same.
Any column level constraint (exception: not null) can be expressed at the table level - but the opposite is not true.
Go for a column level constraint if the constraint is in fact a column constraint else use a table constraint.
It is recommended to always use a column constraint if the constraint applies just to the column (and NOT a table constraint if it only applies to a single column) - you can only do it at the column level.
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