mysql多表查询

登录mysql（ubuntu）

mysql -uroot -pmysql123

source /home/ubuntu/test.sql

 

1.按照oracle语句写

    select e.name, b.name
    from emp e, emp b
    where e.mgr = b.empno;

 

2.改造

    select concat(e.ename, ''s boss is ', b.ename)
    from emp e, emp b
    where e.mgr = b.empno;

 

3.强化，显示king的老板

    select concat(e.ename, ''s boss is ', b.ename)
    from emp e, emp b
    where e.mgr = b.empno; 

 

4.用sql99的语法

    select concat(e.ename, ' 's boss is ', b.ename)
    from emp e left outer join emp b
    on e.mgr = b.empno ; 

 

5.滤空纠正

    select concat(e.ename, '的老板是', ifnull(b.ename, 'himself') )
    from emp e left outer join emp b
    on e.mgr = b.empno;