昨天在做报表的时候，遇到要把类型A的数据和类型B的数据横向放在一个表中展示，两个之间没什么关系，哪个的数据量多也不确定，废了段时间，才折腾出如下的解决方法：

www.2cto.com

需要将SELECT es.name primary_school ,COUNT(DISTINCT esi.stu_id) primary_num FROM……、SELECT es.name AS high_school,COUNT(DISTINCT esi.stu_id) AS high_num FROM……、SELECT COUNT(DISTINCT esi.stu_id) total_num FROM……的结果放到一起，由于结果之间没什么关系，先给获取到的结果添加编号，SELECT @rownumb:=@rownumb+1 AS rownum, resources.* FROM (SELECT @rownumb:=0) r，（……）resources，然后根据编号将三个结果集合并起来：

SELECT c.rownum,b.high_school,b.high_num,a.primary_school,a.primary_num, c.total_num

FROM

(……) b

LEFT JOIN

(……) a

ON a.rownum = b.rownum

LEFT JOIN

(……) c

ON c.rownum = b.rownum

这个结果如果刚好b里面的行数最多是没有问题的，但问题是不知道a、b哪个里面的行数最多，解决这个问题，如果可以用full join就可以直接解决了，但full join对于使用的 mysql版本不可用，采取的方法是用union all将几个left join后得到的结果合并在一起：

SELECT DISTINCT high_school,high_num,primary_school,primary_num, total_num

FROM

(SELECT c.rownum,b.high_school,b.high_num,a.primary_school,a.primary_num, c.total_num

FROM

(……) b

LEFT JOIN

(……) a

ON a.rownum = b.rownum

LEFT JOIN www.2cto.com

(……) c

ON c.rownum = b.rownum

UNION ALL

SELECT c.rownum,b.high_school,b.high_num,a.primary_school,a.primary_num, c.total_num

FROM

(……) a

LEFT JOIN

(……) b

ON a.rownum = b.rownum

LEFT JOIN

(……) c

ON c.rownum = a.rownum

) ee

作者 LemonYang