1、从一个表选出数据更新另一个表（后面的exists一定要加）
update jqhdzt
set shid =
(select shid
from v_plat_userjqinfo t
where jqhdzt.jqbh = t.JQBH
and jqhdzt.shid <> t.SHID)
where shid = ''
and exists (select 1
from v_plat_userjqinfo t
where jqhdzt.jqbh = t.JQBH
and jqhdzt.shid <> t.SHID)
2、查询字段值相同的记录总数量
1）单个字段查询
select t.name,count(1) from tuser t having count(1)>1 group by t.name
2）多个字段查询
SELECT t.spbh,t.spmc,t.shid,COUNT(*) FROM spxx t GROUP BY t.spbh,t.spmc,t.shid HAVING COUNT(*) > 1