Why Does SQL Server Produce an 'Invalid Column Name' Error When Using Aggregate Function Aliases in the HAVING Clause?

SQL Server Alias Restriction in HAVING Clause

In SQL Server, using an alias for an aggregate function in the HAVING clause may result in the "Invalid column name" error. This apparent contradiction stems from the execution flow of a SQL query.

The HAVING clause evaluates after group operations but before the selection process. As such, when the HAVING clause first executes, the alias assigned to the aggregate function, such as 'col7' in the provided code snippet, is not yet recognized by the server.

The order of query execution is as follows:

1. Join tables specified in the FROM clause.
2. Filter rows using the WHERE clause.
3. Group rows based on the GROUP BY clause.
4. Eliminate groups that do not meet the HAVING clause condition.
5. Calculate expressions in the SELECT statement.

Therefore, at the point of HAVING clause evaluation, the server does not recognize 'col7' as a valid column name. This restriction prevents the use of aliases in the HAVING clause to reference aggregate functions.

However, it is possible to use aliases in the ORDER BY clause, as this evaluation occurs after the HAVING clause.

The above is the detailed content of Why Does SQL Server Produce an 'Invalid Column Name' Error When Using Aggregate Function Aliases in the HAVING Clause?. For more information, please follow other related articles on the PHP Chinese website!