e to examine the query carefully to end the problem. Some rewriting of the query, perhaps in conjunction with some index tuning. РWhen tuning a query, the first thing to verify is that the system is using the plan that you expect it to use. It may be that the system is not finding the best plan for a variety of reasons. mon situations that are not handled efficiently by many optimizers follow:РA selection condition involving null values.РSelection conditions involving arithmetic or string expressions or conditions using the or connective. For example, if we have a condition E.age = 2*D.age in the WHERE clause, the optimizer may correctly utilize an available index on E.age but fail to utilize an available index on D.age. Replacing the condition by E.age/2=D.age would reverse the situation.
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