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法律研究使用 MySQL 计数多行并在不同列（和单行）中显示结果
我们首先创建一个表 −
mysql> create table DemoTable1452 -> ( -> FavouriteColor varchar(50) -> ); Query OK, 0 rows affected (2.42 sec)
使用 insert 命令在表中插入一些记录 −
mysql> insert into DemoTable1452 values('Red');
Query OK, 1 row affected (0.31 sec)
mysql> insert into DemoTable1452 values('Yellow');
Query OK, 1 row affected (0.20 sec)
mysql> insert into DemoTable1452 values('Yellow');
Query OK, 1 row affected (0.18 sec)
mysql> insert into DemoTable1452 values('Yellow');
Query OK, 1 row affected (0.23 sec)
mysql> insert into DemoTable1452 values('Blue');
Query OK, 1 row affected (0.42 sec)
mysql> insert into DemoTable1452 values('Blue');
Query OK, 1 row affected (0.33 sec)
mysql> insert into DemoTable1452 values('Red');
Query OK, 1 row affected (0.29 sec)使用 select 语句从表中显示所有记录 −
mysql> select * from DemoTable1452;
这会产生以下输出 −
+----------------+ | FavouriteColor | +----------------+ | Red | | Yellow | | Yellow | | Yellow | | Blue | | Blue | | Red | +----------------+ 7 rows in set (0.00 sec)
以下是计数多行并在不同列中显示结果的查询 −
mysql> select sum(FavouriteColor='Red') as NumberOfRedColor, -> sum(FavouriteColor='Yellow') as NumberOfYellowColor, -> sum(FavouriteColor='Blue') as NumberOfBlueColor -> from DemoTable1452;
这会产生以下输出 −
+------------------+---------------------+-------------------+ | NumberOfRedColor | NumberOfYellowColor | NumberOfBlueColor | +------------------+---------------------+-------------------+ | 2 | 3 | 2 | +------------------+---------------------+-------------------+ 1 row in set (0.27 sec)
更新于：10-12-2019
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