Monday, March 5, 2012

DATEs aren't INTs, at least not any more

I updated a database column today to utilize the SQL 2008 DATE type, upgrading from a SMALLDATETIME which always had a 00:00:00 hh:mm:ss component. I was fairly certain that this would not break any existing code, so I did not perform an exhaustive code search. My mistake.

A function broke with the following message:

Msg 206, Level 16, State 2, Line 1
Operand type clash: date is incompatible with int

"Strange," I thought. "How would an int be getting used as a date?"

Of course there's the basic method of datetime construction from a string: CAST("2012-01-01" as datetime), but that doesn't involve any INTs. Did someone try to use a similar INT (20120101) in place of the string? No, because that would cause an arithmetic overflow...

Well, it turns out that there's another way of using INTs as DATETIMEs:

select cast(CAST('2012-01-10' as datetime) as int)

Apparently this doesn't work any more:

select cast(CAST('2012-01-10' as date) as int)

And this is what was being performed in the function in question:

CASE WHEN io_end > 40947 THEN 1 ELSE 0 END

Which promptly broke when I changed the column to a DATE. So let this be a warning: even something as innocuous as a DATETIME to DATE change needs QA and code search.

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