> >Is this a bug? I can't find an answer to this question in FAQs or archives. > > > >CREATE TABLE aa ( a int); > >INSERT INTO aa VALUES (1),(2),(3),(2),(4),(5),(1),(6),(3); > > > >the following : > >mysql> select a,count(*) as z from aa where z>1 group by a; > > > >displays this error: > >ERROR 1054: Unknown column 'z' in 'where clause' > > > >Why isn't z recognized as a column identifier? > > As others have pointed out, your query requires a HAVING rather than a > WHERE. What hasn't been pointed out, which is worth knowing, is that > column aliases cannot be used in *any* WHERE clause.
...because the WHERE clause is processed first, and the SELECT evaluated later. Similarly GROUP BY is processed before HAVING (which is why that suggestion works). Somewhere there's a 'table' or list showing the sequence that the various clauses are evaluated/executed. Is it in the manual or in your book Paul? If it's online, it would be useful to know where so that a link can be added to answers to such questions... Anyone remember where? =dn --------------------------------------------------------------------- Before posting, please check: http://www.mysql.com/manual.php (the manual) http://lists.mysql.com/ (the list archive) To request this thread, e-mail <[EMAIL PROTECTED]> To unsubscribe, e-mail <[EMAIL PROTECTED]> Trouble unsubscribing? Try: http://lists.mysql.com/php/unsubscribe.php
