MySQL 如何获取列中特定值的数量

首先让我们创建一个表 –

mysql> create table DemoTable
   (
      Id int,
      Name varchar(100)
   );
Query OK, 0 rows affected (1.40 sec)

使用insert命令向表中插入一些记录 –

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;

这将产生下面的输出结果 –

+------+-------+
| 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)

以下是获取列中特定值的计数的查询，即在此处获取“Chris”的计数 –

mysql> select count(*) from DemoTable where Name='Chris';

这将产生下面的输出结果 –

+----------+
| count(*) |
+----------+
| 4        |
+----------+
1 row in set (0.00 sec)

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