Re: SQL 'Select AS' syntax

With INNER JOIN the WHERE for join selection should always be the same. Thus why the QMQRY output was and remains valid, from its availability prior to the JOIN syntax.

I think some other responses were over-presumptive on what should be expected when using WHERE clause to do joins, beyond the INNER JOIN. Albeit I do not recall any more than the simples case of only the join selection being specified. However...

For any other JOIN type [than INNER JOIN] it is probably best to be in the habit of explicitly stating the JOIN ON, because the intent to the query engine may become ambiguous when there are any more selections than the between-file tests to effect the join. In such an ambiguous request, the query engine is not obligated to operate in the way you have assumed it will. The outcome could include a possibly changing result set. For example in an OUTER JOIN, some WHERE clause selections could limit the results prior to the join selection; e.g. because the optimizer found an index that quickly limits the rows to be joined, and because no join selection rules were explicitly stated there is no requirement to order when the selection occurs.

So rather than as a "performance boost", make a habit of avoiding use of the WHERE clause for join to prevent surprises; be explicit in your intentions for the SQL request that is sent to the query engine.

Regards, Chuck