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PostgreSQL HAVING 子句

HAVING 子句可以让我们筛选分组后的各组数据。

WHERE 子句在所选列上设置条件,而 HAVING 子句则在由 GROUP BY 子句创建的分组上设置条件。

语法

下面是 HAVING 子句在 SELECT 查询中的位置:

SELECT

FROM

WHERE

GROUP BY

HAVING

ORDER BY

HAVING 子句必须放置于 GROUP BY 子句后面,ORDER BY 子句前面,下面是 HAVING 子句在 SELECT 语句中基础语法:

SELECT column1, column2

FROM table1, table2

WHERE [ conditions ]

GROUP BY column1, column2

HAVING [ conditions ]

ORDER BY column1, column2

实例

创建 COMPANY 表(下载 COMPANY SQL 文件 ),数据内容如下:

lectcodedb# select * from COMPANY;

id | name | age | address | salary

----+-------+-----+-----------+--------

1 | Paul | 32 | California| 20000

2 | Allen | 25 | Texas | 15000

3 | Teddy | 23 | Norway | 20000

4 | Mark | 25 | Rich-Mond | 65000

5 | David | 27 | Texas | 85000

6 | Kim | 22 | South-Hall| 45000

7 | James | 24 | Houston | 10000

(7 rows)

下面实例将找出根据 NAME 字段值进行分组,并且 name(名称) 字段的计数少于 2 数据:

SELECT NAME FROM COMPANY GROUP BY name HAVING count(name) < 2;

得到以下结果:

name

-------

Teddy

Paul

Mark

David

Allen

Kim

James

(7 rows)

我们往表里添加几条数据:

INSERT INTO COMPANY VALUES (8, 'Paul', 24, 'Houston', 20000.00);

INSERT INTO COMPANY VALUES (9, 'James', 44, 'Norway', 5000.00);

INSERT INTO COMPANY VALUES (10, 'James', 45, 'Texas', 5000.00);

此时,COMPANY 表的记录如下:

id | name  | age | address      | salary

----+-------+-----+--------------+--------

1 | Paul | 32 | California | 20000

2 | Allen | 25 | Texas | 15000

3 | Teddy | 23 | Norway | 20000

4 | Mark | 25 | Rich-Mond | 65000

5 | David | 27 | Texas | 85000

6 | Kim | 22 | South-Hall | 45000

7 | James | 24 | Houston | 10000

8 | Paul | 24 | Houston | 20000

9 | James | 44 | Norway | 5000

10 | James | 45 | Texas | 5000

(10 rows)

下面实例将找出根据 name 字段值进行分组,并且名称的计数大于 1 数据:

lectcodedb-# SELECT NAME FROM COMPANY GROUP BY name HAVING count(name) > 1;

得到结果如下:

name

-------

Paul

James

(2 rows)