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Posted by --CELKO-- on 06/29/07 23:41
>> the standard join and inner join, which one is faster and more reliable? <<
The infixed INNER JOIN and the WHERE clause join produce the same
results. In SQL Server, they also produce the same execution plan and
I thought that the choice was a matter of style. It turns out that is
not true in DB2. A friend asked for help optimizing a very large
query for a report and found out that the older syntax did better.
I am still trying to figure out why this happened. My best guess is
that the infixed operators are required to behave as if they are
executed in left to right order. This is vital or OUTER JOINs, but
should not make a difference for INNER JOINs. But does their
optimizer (which is pretty darn good) get fooled into an acceptable
result with infixed notation, but do more investigation with a FROM
simple clause? I am still waiting to hear back from DB2 experts.
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