How Can I Use Aliases in a SQL WHERE Clause?

Using Aliases in SQL Where Statements

In SQL, we often encounter situations where we need to use aliases to simplify or improve the readability of our queries. An alias assigns a temporary name to a table, column, or expression, allowing us to reference them more conveniently.

Consider the following scenario:

Question: I'm attempting to create an alias in a WHERE statement, but I'm unsure of the syntax. How can I accomplish this in MSSQL 2005?

Example:

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

Answer: Instead of using WHERE, you can employ the HAVING clause to utilize aliases in a WHERE statement:

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

The HAVING clause performs the WHERE condition after the query execution. It's important to use HAVING judiciously to avoid performance issues. By employing HAVING, we still achieve the desired filtering without requiring complex alias usage in the WHERE statement.

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