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  • PHP学习笔记:MySQL数据库的操纵

    Update语句

      Update 表名 set 字段1=值1, 字段2=值2  where  条件

    练习:

    把用户名带  ‘小’的人的密码设置为123456@

    语句:UPDATE crm_user SET userpwd='123456@' WHERE username LIKE '%小%';

    效果

    Group by 、having: 分组查询  having分组查询条件

    语法:SELECT A ,COUNT(B) FROM TABLE GROUP BY A HAVING COUNT(B)>2

    Mysql内置统计函数

    Count(列名)  总计

    Sum(列名)  求和

    Avg(列名)   平均

    Max(列名)  最大值

    Min(列名)   最小值

    举例:

    1.求班级的平均分数

    SELECT class,scores, AVG(scores) FROM jian_scores GROUP BY class;
    

      

    2.求班级的平均分数,并且要求分数高于70分

    SELECT class,scores, AVG(scores) FROM jian_scores GROUP BY class HAVING AVG(scores)>70;
    

      

    联合查询:

    查询jian_scores的id=1,jian_hometown的cityid=5

    SELECT jian_scores.id,jian_scores.students,jian_hometown.city FROM jian_scores,jian_hometown WHERE jian_scores.id='1' AND jian_hometown.cityid='5'

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  • 原文地址:https://www.cnblogs.com/jianqingwang/p/5887831.html
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