MySQL 如何使用一个查询计算某一列中特定值出现的次数

为此，您可以使用GROUP BY子句以及IN()。让我们先创建一个表 –

mysql> create table DemoTable
    -> (
    -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
    -> Name varchar(100)
    -> );
Query OK, 0 rows affected (0.87 sec)

使用insert命令在表中插入一些记录 –

mysql> insert into DemoTable(Name) values('John');
Query OK, 1 row affected (0.23 sec)

mysql> insert into DemoTable(Name) values('Chris');
Query OK, 1 row affected (0.12 sec)

mysql> insert into DemoTable(Name) values('David');
Query OK, 1 row affected (0.23 sec)

mysql> insert into DemoTable(Name) values('Chris');
Query OK, 1 row affected (0.17 sec)

mysql> insert into DemoTable(Name) values('Chris');
Query OK, 1 row affected (0.21 sec)

mysql> insert into DemoTable(Name) values('John');
Query OK, 1 row affected (0.10 sec)

mysql> insert into DemoTable(Name) values('Carol');
Query OK, 1 row affected (0.20 sec)

mysql> insert into DemoTable(Name) values('Sam');
Query OK, 1 row affected (0.19 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  |
+----+-------+
|  1 | John  |
|  2 | Chris |
|  3 | David |
|  4 | Chris |
|  5 | Chris |
|  6 | John  |
|  7 | Carol |
|  8 | Sam   |
+----+-------+
8 rows in set (0.00 sec)

现在，使用单个查询计算特定值在列中出现的次数 –

mysql> select Name,count(*) AS Occurrences from DemoTable
    -> where Name in('John','Chris') group by Name;

这将产生以下输出 –

+-------+-------------+
| Name  | Occurrences |
+-------+-------------+
| John  |           2 |
| Chris |           3 |
+-------+-------------+
2 rows in set (0.00 sec)

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