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, 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 | -12-135 | David | 27 | Texas| 85000 | -12-133 | Teddy | 23 | Norway| 20000 |2 | Allen | 25 | Texas| | -12-131 | 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 | -12-132 | Allen | 25 | Texas| | -12-135 | David | 27 | Texas| 85000 | -12-131 | 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| | -12-135 | David | 27 | Texas| 85000 | -12-134 | Mark | 25 | Rich-Mond | 65000 | -12-131 | Paul | 32 | California | 20000 | 2001-07-133 | 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 | 2001-07-134 | Mark | 25 | Rich-Mond | 65000 | -12-135 | David | 27 | Texas| 85000 | -12-132 | Allen | 25 | Texas| | -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-listFROM table_nameWHERE [ conditions ]GROUP BY column1, column2....columnNORDER 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 | -12-135 | David | 27 | Texas| 85000 | -12-133 | Teddy | 23 | Norway| 20000 |2 | Allen | 25 | Texas| | -12-131 | 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 | 20000David | 85000Paul | 20000Mark | 65000Allen |(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 | -12-135 | David | 27 | Texas| 85000 | -12-133 | Teddy | 23 | Norway| 20000 |2 | Allen | 25 | Texas| | -12-131 | Paul | 32 | California | 20000 | 2001-07-138 | 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 | 20000lili | 10000pasl | 20000David | 85000Paul | 40000Mark | 65000Allen |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 | 10000James | 10000Teddy | 20000pasl | 20000Paul | 40000Mark | 65000David | 85000Allen |(8 行记录)
