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Message Posted: Wed, 18 Aug 2004 @ 18:23:01 GMT

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Possibilities for real differences in query plans (not just formatting) between EXPLAIN and what is already executing:

1) Something changed between the time the executing query was optimized and the time of the EXPLAIN, e.g. index built, updated stats collected.

2) The SQL isn't really the same; for example, EXPLAIN supplies literal values in the WHERE clause but the real query has parameter markers or host variables. (If the actual values are known at optimization time, the optimizer can generate an "aggressive" query plan; otherwise it may focus on minimizing worst case.)

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