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获取不同的值并在MySQL中计数

2024-04-26 01:01:04 352

要获取不同的值并计算它们，可以使用GROUPBY子句。

语法如下

select yourColumnName,count(*) as anyAliasName from yourTableName group by yourColumnName;

为了理解上述语法，让我们创建一个表。创建表的查询如下

mysql> create table GroupByAndCountDemo
   -> (
   -> ClientId int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   -> ClientName varchar(100)
   -> );

使用insert命令在表中插入一些记录。查询如下-

mysql> insert into GroupByAndCountDemo(ClientName) values('John');
mysql> insert into GroupByAndCountDemo(ClientName) values('Carol');
mysql> insert into GroupByAndCountDemo(ClientName) values('Sam');
mysql> insert into GroupByAndCountDemo(ClientName) values('Sam');
mysql> insert into GroupByAndCountDemo(ClientName) values('John');
mysql> insert into GroupByAndCountDemo(ClientName) values('John');
mysql> insert into GroupByAndCountDemo(ClientName) values('John');
mysql> insert into GroupByAndCountDemo(ClientName) values('Sam');
mysql> insert into GroupByAndCountDemo(ClientName) values('Sam');
mysql> insert into GroupByAndCountDemo(ClientName) values('Sam');
mysql> insert into GroupByAndCountDemo(ClientName) values('John');
mysql> insert into GroupByAndCountDemo(ClientName) values('John');
mysql> insert into GroupByAndCountDemo(ClientName) values('John');
mysql> insert into GroupByAndCountDemo(ClientName) values('David');
mysql> insert into GroupByAndCountDemo(ClientName) values('Maxwell');
mysql> insert into GroupByAndCountDemo(ClientName) values('Maxwell');

使用select语句显示表中的所有记录。查询如下-

mysql> select *from GroupByAndCountDemo;

输出如下

+----------+------------+
| ClientId | ClientName |
+----------+------------+
|        1 | John       |
|        2 | Carol      |
|        3 | Sam        |
|        4 | Sam        |
|        5 | John       |
|        6 | John       |
|        7 | John       | 
|        8 | Sam        |
|        9 | Sam        |
|       10 | Sam        |
|       11 | John       |
|       12 | John       |
|       13 | John       |
|       14 | David      |
|       15 | Maxwell    |
|       16 | Maxwell    |
+----------+------------+
16 rows in set (0.00 sec)

现在，让我们获取不同的值并使用以下查询对它们进行计数

mysql> select ClientName,count(*) as TotalCount from GroupByAndCountDemo group by ClientName;

以下是输出

+------------+------------+
| ClientName | TotalCount |
+------------+------------+
| John       |          7 |
| Carol      |          1 |
| Sam        |          5 |
| David      |          1 |
| Maxwell    |          2 |
+------------+------------+
5 rows in set (0.00 sec)

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获取不同的值并在MySQL中计数

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