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极客学院团队出品 · 更新于 2018-11-16 06:00:34

SQL HAVING 子句

HAVING 子句使你能够指定过滤条件,从而控制查询结果中哪些组可以出现在最终结果里面。

WHERE 子句对被选择的列施加条件,而 HAVING 子句则对 GROUP BY 子句所产生的组施加条件。

语法:

下面可以看到 HAVING 子句在 SELECT 查询中的位置:

SELECT
FROM
WHERE
GROUP BY
HAVING
ORDER BY

在 SELECT 查询中,HAVING 子句必须紧随 GROUP BY 子句,并出现在 ORDER BY 子句(如果有的话)之前。带有 HAVING 子句的 SELECT 语句的语法如下所示:

SELECT column1, column2
FROM table1, table2
WHERE [ conditions ]
GROUP BY column1, column2
HAVING [ conditions ]
ORDER BY column1, column2

示例:

考虑 CUSTOMERS 表,表中的记录如下所示:

+----+----------+-----+-----------+----------+
| 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 |
+----+----------+-----+-----------+----------+

下面是一个有关 HAVING 子句使用的实例,该实例将会筛选出出现次数大于或等于 2 的所有记录。

SQL > SELECT ID, NAME, AGE, ADDRESS, SALARY
FROM CUSTOMERS
GROUP BY age
HAVING COUNT(age) >= 2;

其执行结果如下所示:

+----+--------+-----+---------+---------+
| ID | NAME   | AGE | ADDRESS | SALARY  |
+----+--------+-----+---------+---------+
|  2 | Khilan |  25 | Delhi   | 1500.00 |
+----+--------+-----+---------+---------+
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