union运算符,外连接,group分组,between and,having
工具/原料
1
mysql
2
SQLyog
方法/步骤
2
课程表kechengCREATE TABLE `kecheng` ( `id` int(11) NOT NULL, `yuwen` int(11) DEFAULT NULL, `shuxue` int(11) DEFAULT NULL, `yinyu` int(11) DEFAULT NULL, PRIMARY KEY (`id`)) ENGINE=InnoDB DEFAULT CHARSET=utf8
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分组(学生表分组通过班级,查看每班要多少个人)Group bySELECT s.class,COUNT(*) FROM student s GROUP BY s.class
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外连接(学生表和课程表,找到2个表直接id一样的学生)SELECT * FROM student s,kecheng k WHERE s.id=k.id
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between and(找到年龄在20到40之间的学生)SELECT * FROM student s WHERE s.age BETWEEN 20 AND 40
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having(having和group by 一起用了,可以对分组以后的数据进行处理)(以班级分组,每班的学生的年龄之和小于50)SELECT s.class,COUNT(*),SUM(age) FROM student s GROUP BY s.class HAVING SUM(age)<50
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union(合并的字段必须是相同的了)(合并一下id了)
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