sql多表关联更新—用b表字段来更新a表对应的字段

在开发时，如果遇到表需要加字段，那么需要对存量数据刷新这个字段值

1、mysql

--两张表关联
UPDATE JC_COLL_REPAY r
INNER JOIN lc_lm_loan l ON r.loan_no = l.loan_no
SET r.loan_typ = l.tep_cde,
　　r.oper_center = l.bch_cde,
　　r.chnl_cde = l.coopr_cde;

--三张表关联
UPDATE JC_COLL_REPAY r
INNER JOIN lc_lm_loan l ON r.loan_no = l.loan_no
INNER JOIN lc_cust_info i ON l.cust_id = i.cust_id
SET r.loan_typ = l.tep_cde,
　　r.oper_center = l.bch_cde,
　　r.chnl_cde = l.coopr_cde,
　　r.indiv_mobile = i.indiv_mobile;

2、oracle

---三张表关联
update JC_COLL_REPAY r
　　set (r.indiv_mobile,r.loan_typ,r.oper_center,r.chnl_cde) =
　　(select c.indiv_mobile,l.tep_cde,l.bch_cde,l.coopr_cde
　　　　from lc_lm_loan l,lc_cust_info c
　　　　where l.cust_id = c.cust_id and l.loan_no = r.loan_no
　　)
　　where exists (select 1
　　　　from lc_lm_loan l,lc_cust_info c
　　　　where l.cust_id = c.cust_id and l.loan_no = r.loan_no
　　)


---不推荐
update JC_COLL_REPAY r 
set r.loan_typ=(select tep_cde from lc_lm_loan l where r.loan_no=l.loan_no),
　　r.oper_center=(select bch_cde from lc_lm_loan l where r.loan_no=l.loan_no),
　　r.chnl_cde=(select coopr_cde from lc_lm_loan l where r.loan_no=l.loan_no)
where exists (select 1 from a where r.loan_no=l.loan_no)

还可以使用merge into 

merge into TEST_RESULT r
     using (select * from test_major m,test_subject s where m.id = s.sb_ma) ms
     on (r.subject = ms.sb_name)
     when matched then 
     update set r.major = ms.zymc