1. 有时候如果只是向查询不重复的记录，使用distinct即可，一个单词解决
  2. 另外distinct必须放在最前面
  3. distinct a, b, c表示同时作用与三列，而不是作用于a

select a.id,a.spmc,b.jg 凌家塘,c.jg 镇江智慧物价网,d.jg 常州价格通网菜场,e.jg 常州价格通网菜场

from spdz a left join (select jg, spmc from spjg where zqpc=’191106173823’ and sply=’凌家塘’) b
on a.ljt=b.spmc left join (select jg, spmc from spjg where zqpc=’191106173823’ and sply=’镇江智慧物价网’) c
on a.zjwjw=c.spmc left join (select jg, spmc from spjg where zqpc=’191106173823’ and sply=’常州价格通网菜场’) d
on a.czjgt=d.spmc left join (select jg, spmc from spjg where zqpc=’191106173823’ and sply=’常州价格通网菜场’) e
on a.czjgt=e.spmc group by b.jg,c.jg,d.jg,e.jg,a.spmc,a.id order by a.id

等价于

select distinct a.id,a.spmc,b.jg 凌家塘,c.jg 镇江智慧物价网,d.jg 常州价格通网菜场,e.jg 常州价格通网菜场

from spdz a left join (select jg, spmc from spjg where zqpc=’191106173823’ and sply=’凌家塘’) b
on a.ljt=b.spmc left join (select jg, spmc from spjg where zqpc=’191106173823’ and sply=’镇江智慧物价网’) c
on a.zjwjw=c.spmc left join (select jg, spmc from spjg where zqpc=’191106173823’ and sply=’常州价格通网菜场’) d
on a.czjgt=d.spmc left join (select jg, spmc from spjg where zqpc=’191106173823’ and sply=’常州价格通网菜场’) e
on a.czjgt=e.spmc