HAVING子句使您能够指定过滤哪些组结果出现在结果中的条件.
WHERE子句在所选列上放置条件,而HAVING子句为GROUP BY子句创建的组设置条件.
以下代码块显示了HAVING子句在一个中的位置查询.
SELECT FROM WHERE GROUP BY HAVING ORDER BY
HAVING子句必须遵循查询中的GROUP BY子句,并且必须在ORDER BY子句之前使用(如果使用).以下代码块具有SELECT语句的语法,包括HAVING子句 :
SELECT column1,column2 FROM table1,table2 WHERE [条件] GROUP BY column1,column2 HAVING [conditions] ORDER BY column1,column2
考虑具有以下记录的CUSTOMERS表.
+----+----------+-----+-----------+----------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+----------+-----+-----------+----------+ | 1 | Ramesh | 32 | Ahmedabad | 2000.00 | | 2 | Khilan | 25 | Delhi | 1500.00 | | 3 | kaushik | 23 | Kota | 2000.00 | | 4 | Chaitali | 25 | Mumbai | 6500.00 | | 5 | Hardik | 27 | Bhopal | 8500.00 | | 6 | Komal | 22 | MP | 4500.00 | | 7 | Muffy | 24 | Indore | 10000.00 | +----+----------+-----+-----------+----------+
以下是一个示例,它会显示一个类似年龄计数大于或等于2的记录.
SQL > SELECT ID, NAME, AGE, ADDRESS, SALARY FROM CUSTOMERS GROUP BY age HAVING COUNT(age) >= 2;
这会产生以下结果 :
+----+--------+-----+---------+---------+ | ID | NAME | AGE | ADDRESS | SALARY | +----+--------+-----+---------+---------+ | 2 | Khilan | 25 | Delhi | 1500.00 | +----+--------+-----+---------+---------+