mysql 查询小demo

    xiaoxiao2021-03-25  5

     

     

    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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