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What is the difference between a correlated subquery and a regular subquery? |
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Answer» A correlated subquery appears deceptively similar to a regular subquery. The difference is that a regular subquery can be processed from the bottom up. In a regular subquery, results from the lowest query can be determined and used to evaluate the upper-level query. In contrast, in a correlated subquery, the processing is nested; that is, a row from an upper query statement is used in comparison with rows in a lower level query. The key distinction of a correlated subquery is that the lower-level select statements use columns from upper-level statements. |
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