Understanding Oracle aliasing - why isn't an alias not recognized in a query unless wrapped in a second query?

Question

I have a query

SELECT COUNT(*) AS \"CNT\",
       imei
FROM   devices  

which executes just fine. I want to further restrict the query wi

Answer 1

To summarize, this little gem explains:

10 Easy Steps to a Complete Understanding of SQL

A common source of confusion is the simple fact that SQL syntax elements are not ordered in the way they are executed. The lexical ordering is:

SELECT [ DISTINCT ]
FROM
WHERE
GROUP BY
HAVING
UNION
ORDER BY

For simplicity, not all SQL clauses are listed. This lexical ordering differs fundamentally from the logical order, i.e. from the order of execution:

FROM
WHERE
GROUP BY
HAVING
SELECT
DISTINCT
UNION
ORDER BY

As a consequence, anything that you label using "AS" will only be available once the WHERE, HAVING and GROUP BY have already been performed.