How do I use a SELECT list alias in the WHERE or GROUP BY clause?
Many people expect to be able to do this:
However, this results in the following:
The SELECT list is interpreted and evaluated last, so there is no way to use an alias defined there in other clauses of the statement. (One exception is the ORDER BY clause, which is not a T-SQL clause, but rather a cursor operator.)
Joe Celko says the following about the order of operations in a SELECT statement:
This means that a SELECT cannot have more columns than a GROUP BY; but it certainly can have fewer columns.What we can take from all of this, is that you have to repeat your alias expression; so, the above query becomes:
Of course, this can be a pain for more complex formulae, right? Thankfully, there are some workarounds. One is to use a derived table, e.g.
Another workaround is to create a view:
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