Boolean 'NOT' in T-SQL not working on 'bit' datatype?
SqlSql ServerTsqlBoolean OperationsSql Problem Overview
Trying to perform a single boolean NOT operation, it appears that under MS SQL Server 2005, the following block does not work
DECLARE @MyBoolean bit;
SET @MyBoolean = 0;
SET @MyBoolean = NOT @MyBoolean;
SELECT @MyBoolean;
Instead, I am getting more successful with
DECLARE @MyBoolean bit;
SET @MyBoolean = 0;
SET @MyBoolean = 1 - @MyBoolean;
SELECT @MyBoolean;
Yet, this looks a bit a twisted way to express something as simple as a negation.
Am I missing something?
Sql Solutions
Solution 1 - Sql
Use the ~ operator:
DECLARE @MyBoolean bit
SET @MyBoolean = 0
SET @MyBoolean = ~@MyBoolean
SELECT @MyBoolean
Solution 2 - Sql
Your solution is a good one... you can also use this syntax to toggle a bit in SQL...
DECLARE @MyBoolean bit;
SET @MyBoolean = 0;
SET @MyBoolean = @MyBoolean ^ 1;
SELECT @MyBoolean;
Solution 3 - Sql
Subtracting the value from 1 looks like it'll do the trick, but in terms of expressing intent I think I'd prefer to go with:
SET @MyBoolean = CASE @MyBoolean WHEN 0 THEN 1 ELSE 0 END
It's more verbose but I think it's a little easier to understand.
Solution 4 - Sql
To assign an inverted bit, you'll need to use the bitwise NOT operator. When using the bitwise NOT operator, '~', you have to make sure your column or variable is declared as a bit.
This won't give you zero:
Select ~1
This will:
select ~convert(bit, 1)
So will this:
declare @t bit
set @t=1
select ~@t
Solution 5 - Sql
In SQL 2005 there isn't a real boolean value, the bit value is something else really.
A bit can have three states, 1, 0 and null (because it's data). SQL doesn't automatically convert these to true or false (although, confusingly SQL enterprise manager will)
The best way to think of bit fields in logic is as an integer that's 1 or 0.
If you use logic directly on a bit field it will behave like any other value variable - i.e. the logic will be true if it has a value (any value) and false otherwise.
Solution 6 - Sql
BIT is a numeric data type, not boolean. That's why you can't apply boolean operators to it.
SQL Server doesn't have BOOLEAN data type (not sure about SQL SERVER 2008) so you have to stick with something like @Matt Hamilton's solution.
Solution 7 - Sql
Use ABS to get the absolute value (-1 becomes 1)...
DECLARE @Trend AS BIT
SET @Trend = 0
SELECT @Trend, ABS(@Trend-1)