/*+ USE_CONCAT */
Causes all ORs in the statement to be transferred to UNION ALLs.
Use the USE_CONCAT hint to change OR conditions into a UNION ALL. We have found that this hint does not always seem to work as expected. The OR EXISTS in the script below is one case where the USE_CONCAT would speed up the processing considerably.
SELECT /*+ USE_CONCAT */ a.acct_name
FROM accts a
WHERE a.acct_no between (1000 and 2000)
FROM trans t
WHERE a.acct_no = t.acct_no
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