Is there a way to get a boolean without casting in SQL Server?

Question

I've found it very weird that simple code like this is not valid:

select * from table where field=true

The alternative apparently being

select * from table where field='true'

Ok, guess I can live with that. For one reason or another I needed to do something like this recently:

select true as somefield,...

The alternative to get types and everything right was much more ugly though:

select cast('true' as bit) as somefield,...

Am I missing something? Is there actually some built in way to get a true or false value as a boolean without casting?

Solution 1

Sql Server doesn't have a boolean datatype you can store in a table, but it does contain a bit data type you can store.

However, the true keyword you see IS a boolean value. Sql Server only uses the boolean data type for results for its Comparison Operators, which can return three values, TRUE, FALSE, and UNKNOWN.

It is important to know the distinction between the two.

SELECT *
FROM Table
WHERE Field = 1 --Field = true

To store boolean values in a table, use the bit datatype. Use 1 for true, 0 for false, and Null for unknown.

Solution 2

Bits are the datatype most commonly used to represent a boolean in T-SQL. I typically do something like this:

select CAST(1 as bit) as somefield

Solution 3

The values 'TRUE' and 'FALSE' are special strings that can be implicitly converted to variables of type bit. This extract is from the MSDN documentation for bit.

The string values TRUE and FALSE can be converted to bit values: TRUE is converted to 1 and FALSE is converted to 0.

Note that these values appear to be case insensitive.

This is why the where clause in your second code snippet works (I assume that field is defined as a bit).

select * from table where field='true'

Without specifying a target type of bit in any way, 'TRUE' and 'FALSE' are no longer treated as special values and remain simple string values. This is why the cast was required in your third snippet.

select cast('true' as bit) as somefield,...

MSDN states that bit literals (or constants as they are referred to there) are the numbers 0 and 1.

bit constants are represented by the numbers 0 or 1, and are not enclosed in quotation marks. If a number larger than one is used, it is converted to one.

This information may help in some cases but be aware that the literal values 0 and 1 are interpreted as ints rather than bits. The following statements both return 'int' which demonstrates this.

select sql_variant_property(0, 'BaseType')
select sql_variant_property(1, 'BaseType')

Solution 4

I want to add to all current answers only one more method to get a boolean without casting in SQL Server:

DECLARE @myTrue bit = 1;
-- or two lines for old version of SQL Server
-- DECLARE @myTrue bit;
-- SET @myTrue = 1;

SELECT @myTrue AS somefield

Solution 5

Use 1 or 0, assuming your field is of type bit.

select * from table where field=1

select * from table where field=0

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Comments

[Dharman]

While this code may solve the question, including an explanation of how and why this solves the problem would really help to improve the quality of your post, and probably result in more up-votes. Remember that you are answering the question for readers in the future, not just the person asking now. Please edit your answer to add explanations and give an indication of what limitations and assumptions apply.