数据结构
网络
关系型数据库管理系统
操作系统
Java
MS Excel
iOS
HTML
CSS
Android
Python
C 编程
C++
C#
MongoDB
MySQL
Javascript
PHP
物理学
化学
生物学
数学
英语
经济学
心理学
社会学
时尚学
法律学MySQL 查询来选择满足两个独立条件的计数？
为此使用 CASE 语句。让我们首先创建一个表 -
mysql> create table DemoTable -> ( -> StudentMarks int, -> isValid tinyint(1) -> ); Query OK, 0 rows affected (0.68 sec)
使用插入命令在表中插入一些记录 -
mysql> insert into DemoTable values(45,0); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable values(78,1); Query OK, 1 row affected (0.26 sec) mysql> insert into DemoTable values(45,1); Query OK, 1 row affected (0.31 sec) mysql> insert into DemoTable values(78,1); Query OK, 1 row affected (0.22 sec) mysql> insert into DemoTable values(45,0); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable values(82,1); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable values(62,1); Query OK, 1 row affected (0.14 sec)
使用 select 语句从表中显示所有记录 -
mysql> select *from DemoTable;
输出
+--------------+---------+ | StudentMarks | isValid | +--------------+---------+ | 45 | 0 | | 78 | 1 | | 45 | 1 | | 78 | 1 | | 45 | 0 | | 82 | 1 | | 62 | 1 | +--------------+---------+ 7 rows in set (0.00 sec)
以下是选择满足两个独立条件的计数的查询 -
mysql> select StudentMarks, -> sum(case -> when StudentMarks=45 -> then case when isValid = 1 then 1 else 0 end -> else 1 end -> ) AS Freq -> from DemoTable -> group by StudentMarks;
输出
+--------------+------+ | StudentMarks | Freq | +--------------+------+ | 45 | 1 | | 78 | 2 | | 82 | 1 | | 62 | 1 | +--------------+------+ 4 rows in set (0.00 sec)
更新于： 30-7-2019
202 浏览
广告