Re: problem with column alias

You cannot use a column alias in the definition of another column. The
solution is as you found to repeat the expression. Alternative solution is
to define the first column in one CTE (or derived table) and then use the
column in a second CTE.
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Also, it is good to define a valid column name (not a revered keyword) and
then change it to whatever you want in the final SELECT (or client
application).
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Plamen Ratchev