UNION ALL with ROW_NUMBER vs UNION (WAS: "Wow - has anyone used ROW_NUMBER() to get around using a UNION statement when UNION ALL doesn't work??")

From: Taylor, Chris David <ChrisDavid.Taylor_at_ingrambarge.com>
Date: Fri, 12 Aug 2011 13:32:41 -0500
Message-ID: <C5533BD628A9524496D63801704AE56D6A315EC882_at_SPOBMEXC14.adprod.directory>

First, disregard the part about the large TEMP tablespace usage. I think that was coming from the query _before_ I rewrote it to use WITH statements. I'm not seeing the large TEMP usage now.

For each number below, I've included the dbms_xplan information, the row source operations, and the timings.

#1 The original query using WITH statements and UNION
http://pastebin.com/embed_iframe.php?i=0Ht0V4T3 Time: 18 minutes, 38 secs (89,200 rows)

#2 The original query CHANGED from UNION to UNION ALL (only change):
http://pastebin.com/embed_iframe.php?i=JybML3y8 Time: 1 minute, 03 secs (90,227 rows)

#3 The query from #2 CHANGED to include the ROW_NUMBER function to give us the same results as #1:
http://pastebin.com/embed_iframe.php?i=75QJ2ShD Time: 50 secs (89,200 rows)

Chris Taylor
Sr. Oracle DBA
Ingram Barge Company
Nashville, TN 37205
Office: 615-517-3355
Cell: 615-663-1673
Email: chris.taylor_at_ingrambarge.com<mailto:chris.taylor_at_ingrambarge.com>

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Received on Fri Aug 12 2011 - 13:32:41 CDT