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在MySQL中使用条件计算？

2024-05-19 20:47:04 370

要进行计数，请使用聚合函数SUM()并根据条件进行计数，您需要使用WHERE设置条件。让我们首先创建一个表-

create table DemoTable1515
   -> (
   -> ClientId varchar(10),
   -> ClientName varchar(20)
   -> );

使用插入命令在表中插入一些记录-

insert into DemoTable1515 values('CLI-101','Chris');
insert into DemoTable1515 values('CLI-110','David');
insert into DemoTable1515 values('CLI-101','Bob');
insert into DemoTable1515 values('CLI-101','Sam');
insert into DemoTable1515 values('CLI-101','Sam');
insert into DemoTable1515 values('CLI-101','Mike');
insert into DemoTable1515 values('CLI-130','Mike');
insert into DemoTable1515 values('CLI-101','Chris');
insert into DemoTable1515 values('CLI-101','Sam');

使用select语句显示表中的所有记录-

select * from DemoTable1515;

这将产生以下输出-

+----------+------------+
| ClientId | ClientName |
+----------+------------+
| CLI-101  |    Chris   |
| CLI-110  |    David   |
| CLI-101  |      Bob   |
| CLI-101  |      Sam   |
| CLI-101  |      Sam   |
| CLI-101  |     Mike   |
| CLI-130  |     Mike   |
| CLI-101  |     Chris  |
| CLI-101  |      Sam   |
+----------+------------+
9 rows in set (0.00 sec)

这是要计算的查询条件-

select ClientId,sum(ClientName='Sam') as NameOn101Id,count(*) as TotalNameOn101 from DemoTable1515
   -> where ClientId='CLI-101';

这将产生以下输出-

+----------+-------------+----------------+
| ClientId | NameOn101Id | TotalNameOn101 |
+----------+-------------+----------------+
| CLI-101  |           3 |              7 |
+----------+-------------+----------------+
1 row in set (0.00 sec)

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在MySQL中使用条件计算？

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