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why is the query optimizer not able to use the index for deleting when the subquery version, while it is while using the join version? Because the optimizer is/was a bit dumb in that regard. Not only for DELETE and UPDATE but for SELECT statements as well, anything like WHERE column IN (SELECT ...) was not fully optimized. The execution plan usually ...


here is the answers for two of your questions Optimizer is not able to use index because the where clause changes for every row. The delete statement will look something like this after it pass the optimizer delete from VARIABLE_SUBSTITUTION where EXISTS ( select BUILDRESULTSUMMARY_ID from BUILDRESULTSUMMARY where BUILDRESULTSUMMARY.BUILD_KEY = ...

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