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This article mainly introduces how to use exists in oracle. It is very detailed and has a certain reference value. Friends who are interested must finish it!

The usage of exists in oracle

1. Exists is followed by a subquery

2. The following two tables are taken as examples to demonstrate the association between id in table an and aid in table b

3. The function of exists is to check whether the result of the subquery is true, and execute the outer SQL statement if the subquery is true. Exists returns no data, only true or false.

4. If false is returned, the outer SQL statement will not be executed as shown below.

5. His usage is somewhat similar to that of in, but sometimes the efficiency is different when the amount of data is large, but the efficiency is the same when the amount of data is small.

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