update a
set item_cd=c.item_cd
from table_A a inner join Table_b b
on a.item_cd=b.item_cd
inner join Table_c c
on b.item_nm=c.item_nm
set item_cd=c.item_cd
from table_A a inner join Table_b b
on a.item_cd=b.item_cd
inner join Table_c c
on b.item_nm=c.item_nm
From A,B,C
Where A.item_cd=B.item_cd And B.item_nm=C.item_nm
如果表名是Table_A這樣的話Update A Set item_cd=C.item_cd
From Table_A A,Table_B B,Table_C C
Where A.item_cd=B.item_cd And B.item_nm=C.item_nm