Thursday, April 8, 2010

TRUE and FALSE values in SQL Server, BIT datatypes

I had an interesting discussion with my office mate today about return values and the what is TRUE and FALSE. He was wondering what value to put as 'success' on a RETURN statement inside of a stored procedure.

My recommendation to him was to follow the @@ERROR convention of 0 (zero) being the value for success. He rightly asked if 0 did also mean 'false' by convention. That got me into a discussion of the BIT data type in SQL Server and the use of 0 or 1 to indicate true or false.

Well it turns out that SQL Server recoginizes two strings; 'TRUE' and 'FALSE' as valid values that can be assigned and used for comparison of BIT variables. Any other strings will cause a conversion error.

To illustrate the point see the code at the bottom of this entry. Why would you ever use the strings 'TRUE' and 'FALSE' versus 1 or 0?

The answer CLARITY!

Regards, Dave

--
--
declare @theBit bit
set @theBit = 'TRUE'
if @theBit = 'TRUE' print 'It is true'
if @theBit = 'FALSE' print 'It is false'
--
print '--Next case--'
set @theBit = 'FALSE'
if @theBit = 'TRUE' print 'It is true'
if @theBit = 'FALSE' print 'It is false'
--
--This will cause a conversion error
--
set @theBit = 'BLAH'
--

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