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Fisrt optimizer takes one of best plans - not the best. This is because when the optimizer works the time for calculating the best plan can be bigger than the time it saves during the execution. And yes, optimizer works based on statistics. So if your statistics is old enough optimizer will create plan suiatble for that statistics - i.e. for the moment of ...


The optimizer strives to get a plan that is "good enough", and this is not always the optimal one. A very common reason is a too complex query. Breaking it down to a few queries helps the optimizer choose a better plan. In some cases, too many indexes on a table can also cause this, as the optimizer might use an index that is not the best one because as ...

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