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如何通过单个MySQL查询计算列中特定值的出现次数？

2024-05-02 22:17:04 420

为此，您可以将GROUPBY子句与一起使用IN()。让我们首先创建一个表-

mysql> create table DemoTable
   -> (
   -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   -> Name varchar(100)
   -> );

使用插入命令在表中插入一些记录-

mysql> insert into DemoTable(Name) values('John');

mysql> insert into DemoTable(Name) values('Chris');

mysql> insert into DemoTable(Name) values('David');

mysql> insert into DemoTable(Name) values('Chris');

mysql> insert into DemoTable(Name) values('Chris');

mysql> insert into DemoTable(Name) values('John');

mysql> insert into DemoTable(Name) values('Carol');

mysql> insert into DemoTable(Name) values('Sam');

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，通过单个查询计算一列中特定值的出现次数-

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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如何通过单个MySQL查询计算列中特定值的出现次数？

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