How Can I Use Aliases in MSSQL WHERE Clauses?

MSSQL Where Statement Aliasing

In MSSQL, using aliases in where statements is not supported. However, there is an alternative solution to achieve a similar effect.

Using the HAVING Clause

Instead of using a where statement, you can utilize the having clause. The having clause performs a filter after the query has been executed, which allows you to compare an alias or expression to a specified value.

Example

Consider the following query:

SELECT SUBSTRING(Column1, 1, 4) + SUBSTRING(Column1, 4, 3)  AS Col1
FROM MyTable
WHERE Col1 = 'MySearch'

To use an alias with this query, rewrite it as follows:

SELECT
    SUBSTRING(Column1, 1, 4) + SUBSTRING(Column1, 4, 3)  AS Col1
FROM
    MyTable
HAVING
    Col1 = 'MySearch'

Understanding the HAVING Clause

The having clause compares the aliased expression Col1 with the value 'MySearch' after the query has been executed. This ensures that only rows that meet the specified condition are returned.

Caution

While using the having clause provides a workaround for aliases in where statements, it's important to use it cautiously. Its use can impact performance if applied in scenarios where it's unnecessary.

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