发表于： 2017-09-07 22:24:04
2 785
今天完成的事情:
学习mysql的查询,因为今天事比较多,所以学的不多,不过还是有收获的,做了点笔记
stuName等于混球
select * from t_student t1 where t1.stuName='混球';
age>17
select * from t_student t1 where t1.age>17;
sex='男'
select * from t_student t1 where t1.sex='男';
age等于18或23
select * from t_student t1 where t1.age IN ('18','23');
age不等于18或23
select * from t_student t1 where t1.age NOT IN ('18','23');
age在10-18(BETWEEN 之间)
select * from t_student t1 where t1.age BETWEEN 10 AND 18;
age不在10-18的(BETWEEN 之间)
select * from t_student t1 where t1.age NOT BETWEEN 10 AND 18;
模糊查询
select * from t_student t1 where t1.stuName LIKE '%混%';
sex为空
select * from t_student t1 where t1.sex is not NULL;
三年级并且17岁的学生
select * from t_student t1 where t1.age=17 AND gradeName='三年级';
三年级或者17岁的学生
select * from t_student t1 where t1.age=17 OR gradeName='三年级';
按age从小到大排序
select * from t_student ORDER BY age ASC;
按age从大到小排序
select * from t_student ORDER BY age DESC;
去掉查询重复的结果(DISTINCT 不同的)
select DISTINCT gradeName from t_student;
查询每个年级的所有学生姓名
select gradeName,GROUP_CONCAT(stuName) FROM t_student GROUP BY gradeName;
函数
以某个字段分组...GROUP BY 字段名
COUNT(*)
SELECT COUNT(*) FROM t_grade;
求张三的总分(SUM 求和)
SELECT stuName,SUM(score) FROM t_grade WHERE stuName="张三";
以名字分组
SELECT stuName,SUM(score) FROM t_grade GROUP BY stuName;
求平均分(AVG)
SELECT stuName,AVG(score) FROM t_grade GROUP BY stuName;
链接查询
内连接
SELECT t1.stuName,t1.course,t2.score FROM t_grade t1,t_student t1.score,t2.sex where t1.stuName=t2.stuName;
外连接
...
遇到的困难:
无
收获:
熟练使用mysql查询指令
明天的计划:
明天复盘评审
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