PgSQL——学习笔记八： ORDER BY 子句：排序 & GROUP BY 语句：分组

PostgreSQL ORDER BY 语句：对一列或多列数据进行升序（ASC）或降序（DESC）排列。在 PostgreSQL 中，ORDER BY 用于对一列或者多列数据进行升序（ASC）或者降序（DESC）排列。//ORDER BY 子句的基础语法如下：SELECT column-listFROM table_name[WHERE condition][ORDER BY column1, c

艺晨星

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艺晨星 · 2022-05-16 22:39:23 发布

PostgreSQL ORDER BY 语句：对一列或多列数据进行升序（ASC）或降序（DESC）排列。

在 PostgreSQL 中，ORDER BY 用于对一列或者多列数据进行升序（ASC）或者降序（DESC）排列。

//ORDER BY 子句的基础语法如下：
SELECT column-list
FROM table_name
[WHERE condition]
[ORDER BY column1, column2, .. columnN] [ASC | DESC];

您可以在 ORDER BY 中使用一列或者多列，但是必须保证要排序的列必须存在。
ASC 表示升序，DESC 表示降序。
实例：

mydb=# select * from COMPANY;
 id | name  | age |                      address                       | salary | join_date
----+-------+-----+----------------------------------------------------+--------+------------
  4 | Mark  |  25 | Rich-Mond                                          |  65000 | 2007-12-13
  5 | David |  27 | Texas                                              |  85000 | 2007-12-13
  3 | Teddy |  23 | Norway                                             |  20000 |
  2 | Allen |  25 | Texas                                              |        | 2007-12-13
  1 | Paul  |  32 | California                                         |  20000 | 2001-07-13
(5 行记录)

//将对结果根据 AGE 字段值进行升序排列：
mydb=# SELECT * FROM COMPANY ORDER BY AGE ASC;
 id | name  | age |                      address                       | salary | join_date
----+-------+-----+----------------------------------------------------+--------+------------
  3 | Teddy |  23 | Norway                                             |  20000 |
  4 | Mark  |  25 | Rich-Mond                                          |  65000 | 2007-12-13
  2 | Allen |  25 | Texas                                              |        | 2007-12-13
  5 | David |  27 | Texas                                              |  85000 | 2007-12-13
  1 | Paul  |  32 | California                                         |  20000 | 2001-07-13
(5 行记录)

//将对结果根据 NAME 字段值和 SALARY 字段值进行升序排序：
mydb=# SELECT * FROM COMPANY ORDER BY NAME, SALARY ASC;
 id | name  | age |                      address                       | salary | join_date
----+-------+-----+----------------------------------------------------+--------+------------
  2 | Allen |  25 | Texas                                              |        | 2007-12-13
  5 | David |  27 | Texas                                              |  85000 | 2007-12-13
  4 | Mark  |  25 | Rich-Mond                                          |  65000 | 2007-12-13
  1 | Paul  |  32 | California                                         |  20000 | 2001-07-13
  3 | Teddy |  23 | Norway                                             |  20000 |
(5 行记录)

//将对结果根据NAME字段值进行降序排列：
mydb=# SELECT * FROM COMPANY ORDER BY NAME DESC;
 id | name  | age |                      address                       | salary | join_date
----+-------+-----+----------------------------------------------------+--------+------------
  3 | Teddy |  23 | Norway                                             |  20000 |
  1 | Paul  |  32 | California                                         |  20000 | 2001-07-13
  4 | Mark  |  25 | Rich-Mond                                          |  65000 | 2007-12-13
  5 | David |  27 | Texas                                              |  85000 | 2007-12-13
  2 | Allen |  25 | Texas                                              |        | 2007-12-13
(5 行记录)

PostgreSQL GROUP BY 语句：与SELECT 语句一起使用，对相同的数据进行分组

在 PostgreSQL 中，GROUP BY 语句和 SELECT 语句一起使用，用来对相同的数据进行分组。
注意：GROUP BY 在一个 SELECT 语句中，放在 WHRER 子句的后面，ORDER BY 子句的前面。

//下面给出了 GROUP BY 子句的基本语法:
SELECT column-list
FROM table_name
WHERE [ conditions ]
GROUP BY column1, column2....columnN
ORDER BY column1, column2....columnN

注意：GROUP BY 子句必须放在 WHERE 子句中的条件之后，必须放在 ORDER BY 子句之前。
在 GROUP BY 子句中，你可以对一列或者多列进行分组，但是被分组的列必须存在于列清单中。

mydb=# select * from COMPANY;
 id | name  | age |                      address                       | salary | join_date
----+-------+-----+----------------------------------------------------+--------+------------
  4 | Mark  |  25 | Rich-Mond                                          |  65000 | 2007-12-13
  5 | David |  27 | Texas                                              |  85000 | 2007-12-13
  3 | Teddy |  23 | Norway                                             |  20000 |
  2 | Allen |  25 | Texas                                              |        | 2007-12-13
  1 | Paul  |  32 | California                                         |  20000 | 2001-07-13
(5 行记录)

//将根据 NAME 字段值进行分组，找出每个人的工资总额：
mydb=# SELECT NAME, SUM(SALARY) FROM COMPANY GROUP BY NAME;
 name  |  sum
-------+-------
 Teddy | 20000
 David | 85000
 Paul  | 20000
 Mark  | 65000
 Allen |
(5 行记录)

//在 CAMPANY 表中添加几条记录后：
mydb=# select * from COMPANY;
 id | name  | age |                      address                       | salary | join_date
----+-------+-----+----------------------------------------------------+--------+------------
  4 | Mark  |  25 | Rich-Mond                                          |  65000 | 2007-12-13
  5 | David |  27 | Texas                                              |  85000 | 2007-12-13
  3 | Teddy |  23 | Norway                                             |  20000 |
  2 | Allen |  25 | Texas                                              |        | 2007-12-13
  1 | Paul  |  32 | California                                         |  20000 | 2001-07-13
  8 | Paul  |  24 | Houston                                            |  20000 |
  6 | pasl  |  24 | Hou                                                |  20000 |
  7 | lili  |  23 | hy                                                 |  10000 |
  9 | James |  44 | Norway                                             |   5000 |
 10 | James |  45 | Texas                                              |   5000 |
(10 行记录)

//根据 NAME 字段值进行分组，找出每个客户的工资总额：
mydb=# SELECT NAME, SUM(SALARY) FROM COMPANY GROUP BY NAME;
 name  |  sum
-------+-------
 Teddy | 20000
 lili  | 10000
 pasl  | 20000
 David | 85000
 Paul  | 40000
 Mark  | 65000
 Allen |
 James | 10000
(8 行记录)

//将 ORDER BY 子句与 GROUP BY 子句一起使用：
mydb=# SELECT NAME, SUM(SALARY) FROM COMPANY GROUP BY NAME ORDER BY sum ASC;
 name  |  sum
-------+-------
 lili  | 10000
 James | 10000
 Teddy | 20000
 pasl  | 20000
 Paul  | 40000
 Mark  | 65000
 David | 85000
 Allen |
(8 行记录)