如何使用 MySQL 获取某一列中特定值的数量?
mysqlmysqli database
首先我们创建一个表 −
mysql> create table DemoTable ( Id int, Name varchar(100) ); Query OK, 0 rows affected (1.40 sec)
使用 insert 命令在表中插入一些记录 −
mysql> insert into DemoTable values(100,'John'); Query OK, 1 row affected (0.44 sec) mysql> insert into DemoTable values(101,'Chris'); Query OK, 1 row affected (0.10 sec) mysql> insert into DemoTable values(102,'Chris'); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable values(103,'Chris'); Query OK, 1 row affected (1.05 sec) mysql> insert into DemoTable values(104,'David'); Query OK, 1 row affected (0.19 sec) mysql> insert into DemoTable values(105,'Chris'); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable values(106,'Carol'); Query OK, 1 row affected (0.24 sec) mysql> insert into DemoTable values(107,'Bob'); Query OK, 1 row affected (0.18 sec)
使用 select 语句显示表中的所有记录 −
mysql> select *from DemoTable;
这将产生以下输出 −
+------+-------+ | Id | Name | +------+-------+ | 100 | John | | 101 | Chris | | 102 | Chris | | 103 | Chris | | 104 | David | | 105 | Chris | | 106 | Carol | | 107 | Bob | +------+-------+ 8 rows in set (0.00 sec)
以下查询用于获取某一列中特定值的计数，即此处的‘Chris’ −
mysql> select count(*) from DemoTable where Name='Chris';
这将产生以下输出 −
+----------+ | count(*) | +----------+ | 4 | +----------+ 1 row in set (0.00 sec)
