Can a unique index have more than one null value? If not,
what error code is given if an attempt is made to insert
more than one null value?
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Answer / mani
Unique index can have null values and no null value is equal
to another null value.
i don't know if it raises an error or not when you insert a
null value.
Null value acceptance in the column is again based on the
definition given for the column whether it can accept null
values or not.
| Is This Answer Correct ? | 5 Yes | 2 No |
Answer / sri
Null value will allow only one null (That is maximum) as
per DB2 stds. If we try to insert more we get error -305.
| Is This Answer Correct ? | 2 Yes | 5 No |
Answer / ratheesh
No. A SQLCODE of -803 (duplicate insert) will be returned.
| Is This Answer Correct ? | 0 Yes | 6 No |
SET is the ANSI standard for variable assignment, SELECT is not. SET can only assign one variable at a time, SELECT can make multiple assignments at once. If assigning from a query, SET can only assign a scalar value. If the query returns multiple values/rows then SET will raise an error. SELECT will assign one of the values to the variable and hide the fact that multiple values were returned (so you'd likely never know why something was going wrong elsewhere - have fun troubleshooting that one) When assigning from a query if there is no value returned then SET will assign NULL, where SELECT will not make the assignment at all (so the variable will not be changed from it's previous value) As far as speed differences - there are no direct differences between SET and SELECT. However SELECT's ability to make multiple assignments in one shot does give it a slight speed advantage over SET.
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