Having Object

The HAVING clause in SQL is used to filter grouped records after aggregation. The HAVING clause is optional, and its syntax is similar to that of the WHERE clause.

The mapping of the HAVING clause is implemented through a Having object.

The mapping process reuses the query object mapping algorithm, supporting both prefix mapping and suffix mapping for field mapping. For example, defining a field avgScoreGe in a Having object will be mapped to:

HAVING avg(score) >= ?

In Java, a Having object implements an empty interface Having to mark that it is used for constructing the HAVING clause. Meanwhile, the Having object can extend a query object, and the query object can extend PageQuery, forming a three-level structure.

• Fields in PageQuery are used to construct the ORDER BY and pagination clauses;

• Fields in the query object are used to construct the WHERE clause;

• Fields in the Having object are used to construct the HAVING clause.