PostgreSQL - Having语句

HAVING子句允许无涯教程在函数的输出满足某些条件的情况下选择特定的行，WHERE子句将条件放置在所选列上，而HAVING子句将条件放置在GROUP BY子句创建的组上。

Having - 语法

以下是HAVING子句在SELECT查询中的位置-

无涯教程网

SELECT
FROM
WHERE
GROUP BY
HAVING
ORDER BY

HAVING子句必须在查询中的GROUP BY子句之后，并且还必须在ORDER BY子句(如果使用)之前。以下是SELECT语句的语法，包括HAVING子句-

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

Having - 示例

考虑表 COMPANY 具有以下记录:

# select * from COMPANY;
 id | name  | age | address   | salary
----+-------+-----+-----------+--------
  1 | Paul  |  32 | California|  20000
  2 | Learnfk |  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)

以下是一个示例，它将显示名称计数小于2的记录-

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

这将产生以下输出-

链接：https://www.learnfk.comhttps://www.learnfk.com/postgresql/postgresql-having-clause.html

来源：LearnFk无涯教程网

  name
 -------
  Teddy
  Paul
  Mark
  David
  Learnfk
  Kim
  James
(7 rows)

现在，让无涯教程使用以下INSERT语句在COMPANY表中再创建三个记录-

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);

现在，无涯教程的表具有以下重复名称的记录-

  id | name  | age | address      | salary
 ----+-------+-----+--------------+--------
   1 | Paul  |  32 | California   |  20000
   2 | Learnfk |  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)

以下是示例，它将显示名称计数大于1的记录-

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

这将产生以下输出-

链接：https://www.learnfk.comhttps://www.learnfk.com/postgresql/postgresql-having-clause.html

来源：LearnFk无涯教程网

 name
-------
 Paul
 James
(2 rows)