批量更新sql 批量update sql

批量更新sql |批量update sql
批量更新表時，update乙個表的列時，需要依賴另外的表，這種依賴可以是where條件子句，也可以要update的field的值依賴另外的表
通常有兩種做法
1.使用儲存過程
2.在程式**裡逐條迴圈執行
這裡給出一種更高效、簡潔的做法，批量更新sql ，一句sql就可以替代麻煩的迴圈過程，有ms sqlserver、oracle、db2下的寫法
--關鍵點：t4和t1是同乙個table，primary key肯定也是同乙個，
--並以它進行關聯，這樣在 select語句裡即可引用到要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));

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