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  • mysql 查询小demo

    两张表的的结构如下,需求是写出从one表到two表和从two表到one表的查询转换。

    create table student_one(
    	name varchar(50) default '' not null,
    	type varchar(10) not null default 0,
    	score float(5,2) not null default 0.00
    )Engine=innodb;
    
    
    create table student_two(
    	name varchar(50) default '' not null,
    	math  float(5,2) not null default 0.00,
    	english float(5,2) not null default 0.00,
    	chinese float(5,2) not null default 0.00
    )Engine=innodb;
    

      目前表中数据如下所示

    以表one为基准查出表two的格式的语句如下:

    select a.name,a.score as 'math',b.score as 'chinese',c.score as 'english'
    from student_one a join student_one b join student_one c 
    on a.name=b.name and a.name=c.name and b.name=c.name 
    where a.type='math' and b.type='chinese' and c.type='Engine';
    

    查询结果如下图所示:

      

    以表two为基准查出表one的格式的语句如下:

    select a.name,a.math as score,'math' as type from student_two a 
    union
    select b.name,b.english as score,'english' as type from student_two b 
    union
    select c.name,c.chinese as score,'chinese' as type from student_two c;
    

      查询结果如下:

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  • 原文地址:https://www.cnblogs.com/ddddemo/p/6637427.html
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