CODEWITHSUNDEEP
sqlsql-servert-sqlboolean-operations
Joannes Vermorel
Joannes Vermorel

Reputation: 9245

Boolean 'NOT' in T-SQL not working on 'bit' datatype?

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?

Upvotes: 88

Views: 93622

Answers (7)

FistOfFury
FistOfFury

Reputation: 7155

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

Upvotes: 17

Stephen B Craver
Stephen B Craver

Reputation: 41

Use ABS to get the absolute value (-1 becomes 1)...

DECLARE @Trend AS BIT
SET @Trend = 0
SELECT @Trend, ABS(@Trend-1)

Upvotes: 4

Keith
Keith

Reputation: 155692

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.

Upvotes: 10

Jonas Lincoln
Jonas Lincoln

Reputation: 9767

Use the ~ operator:

DECLARE @MyBoolean bit
SET @MyBoolean = 0
SET @MyBoolean = ~@MyBoolean
SELECT @MyBoolean

Upvotes: 165

aku
aku

Reputation: 123984

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.

Upvotes: 5

Matt Hamilton
Matt Hamilton

Reputation: 204169

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.

Upvotes: 22

Galwegian
Galwegian

Reputation: 42227

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;

Upvotes: 25

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