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Dynamic SQL of MyBatis
Operation of dynamic sql+ account amount
Generally, if it is a delete statement, we delete it according to the primary key, because the primary key is unique.
Sum() query
When we query the total statistics, it may return null, so you can't use the basic data type to receive, you should use the encapsulated type to receive data, if you use the basic type, a null pointer error will be reported
dynamic sql operation