In SQL Server, the Boolean data type is not included. However, SQL Server provides an alternative data type called “bit” that can be used to store boolean values. The bit data type can store three values: 1, 0, and NULL. This data type is more efficient than the Boolean data type used by other databases because it only uses 1 bit to store the data.

Working with the Bit Data Type

To declare a variable with the bit data type, you can use the following syntax:

DECLARE @myBoolean bit;

You can set the value of the bit variable to true or false using the values 1 and 0, respectively. For example:

SET @myBoolean = 1; -- true
SET @myBoolean = 0; -- false

You can also set the bit variable to NULL if necessary:

SET @myBoolean = NULL;

To select the value of a bit variable, you can use the SELECT statement:

SELECT @myBoolean;

The result will be 1 for true, 0 for false, and NULL for NULL.

Replacing 0 and 1 with True and False

If you want to display the values as “true” and “false” instead of 0 and 1, you can use the CASE statement:

SELECT CASE WHEN @myBoolean = 1 THEN 'true' WHEN @myBoolean = 0 THEN 'false' ELSE NULL END;

This will return “true” for 1, “false” for 0, and NULL for NULL.

Creating a Table with a Bit Column

To create a table with a bit column, you can use the following syntax:

CREATE TABLE myTable (
    id int,
    isTrue bit
);

You can then insert data into the table using the values 1, 0, and NULL:

INSERT INTO myTable VALUES (1, 1), (2, 0), (3, NULL);

Working with Bit Columns in Queries

When working with bit columns in queries, you can use the following syntax:

SELECT id, isTrue FROM myTable WHERE isTrue = 1;

This will return the rows where the isTrue column is true (1).

You can also use the values ‘true’ and ‘false’ instead of 0 and 1, but this practice is not recommended:

SELECT id, isTrue FROM myTable WHERE isTrue = 'true';

If you want to select rows where the isTrue column is NULL, you need to use the IS operator:

SELECT id, isTrue FROM myTable WHERE isTrue IS NULL;

Converting Bit to Other Data Types

If you need to convert a bit variable to another data type, you can use the CONVERT function:

SELECT CONVERT(int, @myBoolean); -- convert bit to int

Alternatively, you can use the CAST function:

SELECT CAST(@myBoolean AS varchar(5)); -- convert bit to varchar

Using Bit Variables in Stored Procedures

Bit variables can also be used in stored procedures. You can create a stored procedure that accepts a bit parameter and performs operations based on its value:

CREATE PROCEDURE myProcedure
    @myBoolean bit
AS
BEGIN
    SELECT * FROM myTable WHERE isTrue = @myBoolean;
END;

To execute the stored procedure, you can use the EXEC statement:

EXEC myProcedure @myBoolean = 1;

This will return the rows where the isTrue column is true (1).

In summary, the bit data type in SQL Server is a more efficient alternative to the Boolean data type used by other databases. It allows you to store boolean values using 1 bit of storage. You can use the bit data type in variables, tables, queries, and stored procedures. Remember to use the values 1 and 0 for true and false, and NULL for null values.