DB2批量更新

aa(id,qty) ,bb(id,qty,loc_id(货架号))两个表.目的是把aa.qty=bb.qty
db2 update aa set qty=(select qty from bb where bb.id=aa.id and bb.loc_id=9) where exists (select 1 from bb where bb.id=aa.id and bb.loc_id=9)
-----------------------------------------------------------------------------------------------
如果不加where exits这个条件,那么会把aa表中aa._id!=bb._id的那部分aa.qty数据给update成null.

 

 

 批量更新表时，update一个表的列时，需要依赖另外的表，这种依赖可以是where条件子句，也可以要update的field的值依赖另外的表
   通常有两种做法
   1.使用存储过程
   2.在程序代码里逐条循环执行
这里给出一种更高效、简洁的做法，批量更新SQL ，一句SQL就可以替代麻烦的循环过程，有MS SQLServer、Oracle、DB2下的写法
--关键点：t4和t1是同一个table，primary key肯定也是同一个，
--并以它进行关联，这样在 select语句里即可引用到要update的表的fields 

UPDATE Table1 AS t1
SET (Field1,Field2) = (SELECT Field21, Field22
                       FROM Table2 t2
                            INNER JOIN Table3 t3
                                 ON t3.Field31 = t2.Field23
                            INNER JOIN Table4 t4
                                 ON t3.Field32 = t4.Filed41
                       WHERE t2.Field24 >= ''
                                      AND t1.fId = t4.fId);
----------------------------MS SQLServer --------------------------------------

UPDATE t1
SET Field1 = Field21, Field2 = Field22
FROM Table2 t2
         INNER JOIN Table3 t3
              ON t3.Field31 = t2.Field23
         INNER JOIN Table4 t4
              ON t3.Field32 = t4.Filed41
WHERE ((t2.Field24 >= '')
                  AND t1.fId = t4.fId);
----------------------------Oracle --------------------------------------------

UPDATE Table1 t1
SET (Field1,Field2) = (SELECT Field21, Field22
                       FROM Table2 t2
                            INNER JOIN Table3 t3
                                 ON t3.Field31 = t2.Field23
                            INNER JOIN Table4 t4
                                 ON t3.Field32 = t4.Filed41
                       WHERE ((t2.Field24 >= '')
                                 AND t1.fId = t4.fId))
WHERE EXISTS (SELECT Field21, Field22
              FROM Table2 t2
                   INNER JOIN Table3 t3
                        ON t3.Field31 = t2.Field23
                   INNER JOIN Table4 t4
                        ON t3.Field32 = t4.Filed41
              WHERE ((t2.Field24 >= '')
                               AND t1.fId = t4.fId));
---------------------------------DB2 ------------------------------------------

UPDATE Table1 AS t1
SET (Field1,Field2) = (SELECT Field21, Field22
                       FROM Table2 t2
                            INNER JOIN Table3 t3
                                 ON t3.Field31 = t2.Field23
                            INNER JOIN Table4 t4
                                 ON t3.Field32 = t4.Filed41
                       WHERE ((t2.Field24 >= '')
                                         AND t1.fId = t4.fId))
WHERE EXISTS (SELECT Field21, Field22
              FROM Table2 t2
                   INNER JOIN Table3 t3
                        ON t3.Field31 = t2.Field23
                   INNER JOIN Table4 t4
                        ON t3.Field32 = t4.Filed41
              WHERE ((t2.Field24 >= '')
                                AND t1.fId = t4.fId));

 

Update SJCJ_DA_K_Y_M_ORG_RETAIL_BRAND A
set (A.DEMAND_L,A.ORDER_L,A.SELL_AMOUNT_L,A.SELL_MONEY_L,A.GROSS_PROFIT_L) =
(select  SUM(B.DEMAND), SUM(B.ORDER),  
          SUM(B.SELL_AMOUNT), 
          SUM(B.SELL_MONEY),     
          SUM(B.GROSS_PROFIT)
 From SJCJ_DA_K_Y_M_ORG_RETAIL_BRAND B
    WHERE  B.ORG_CODE='11150101' AND B.IS_USE='9999'
  AND A.Y = B.Y-1 AND
   A.M = B.M   AND
   A.RETAIL_ID=B.RETAIL_ID AND A.BRAND_ID=B.BRAND_ID
AND A.STOCK_DATE>='2012-03-01' AND A.STOCK_DATE<='2012-03-31'
)

where exists (
select  1
 From SJCJ_DA_K_Y_M_ORG_RETAIL_BRAND B
    WHERE  B.ORG_CODE='11150101'
  AND A.Y = B.Y-1 AND
   A.M = B.M  
   AND A.ORG_CODE=B.ORG_CODE
   AND   A.RETAIL_ID=B.RETAIL_ID AND A.BRAND_ID=B.BRAND_ID
   AND A.STOCK_DATE>='2012-03-01' AND A.STOCK_DATE<='2012-03-31'
)
返回必须是一行数据