如果我從以下查詢中刪除exists語句,輸出如何更改?
在oracle中存在vs不存在
UPDATE AR_CRDT C
set (OPERATOR_ID,UPDT_TS) = (SELECT AD.OPERATOR_ID,sysdate
FROM
(
Select A.*
FROM AR1_CUSTOMER_CREDIT A
)AD
WHERE AD.CREDIT_ID = C.CRDT_ID
)
where exists (SELECT 1
FROM
(
Select A.*
FROM AR1_CUSTOMER_CREDIT A
)AD
WHERE AD.CREDIT_ID = C.CRDT_ID
);
這類似於內連接和左外連接之間的區別。它實際上**是**內部連接和外部連接之間的區別,如果您將'update'重寫爲連接的更新,如下所述:http://stackoverflow.com/documentation/oracle/8061/update- with-joins#t = 201702151427027709587 – mathguy