Question

我知道此查询中的（+）运算符：

SELECT 
   * 
FROM
   TBL_TEST t, TBL_TEST_2 t2
WHERE
   t.FIELD (+) = t2.FIELD;

但是（+）运算符在这样的查询中做了什么：

SELECT 
   * 
FROM
   TBL_TEST t
WHERE
   t.FIELD (+) = 2;

我不知道......

有人可以解释一下吗？

Answer 1

我有一个例子

    select * from xxtest
V_ID    V_NAME  V_ADDRESS
5   PriceList   349FDAFD34M
7   PriceList   349FDAFD34M
7   Footer1 349FDAFD34M
5   Footer1 349FDAFD34M
5   Header1 349FDAFD34M
7   Header1 349FDAFD34M




 select * from xxtest2
V_ID    V_NAME  V_ADDRESS
7   Header1 349FDAFD34M

查询01

    select * 
    from xxtest aa, xxtest2 bb 
    where aa.v_id = bb.v_id(+) and bb.v_id(+) = 7
V_ID    V_NAME  V_ADDRESS   V_ID    V_NAME  V_ADDRESS
7   PriceList   349FDAFD34M 7   Header1 349FDAFD34M
7   Footer1 349FDAFD34M 7   Header1 349FDAFD34M
7   Header1 349FDAFD34M 7   Header1 349FDAFD34M
5   PriceList   349FDAFD34M  -   -   - 
5   Footer1 349FDAFD34M  -   -   - 
5   Header1 349FDAFD34M  -   -   -

查询02

    select * 
    from xxtest aa, xxtest2 bb 
    where aa.v_id = bb.v_id(+) and bb.v_id = 7
V_ID    V_NAME  V_ADDRESS   V_ID    V_NAME  V_ADDRESS
7   PriceList   349FDAFD34M 7   Header1 349FDAFD34M
7   Footer1 349FDAFD34M 7   Header1 349FDAFD34M
7   Header1 349FDAFD34M 7   Header1 349FDAFD34M

希望它能帮到你。

Answer 2

强制Oracle承认它的外连接

select *
from ( select 1 n from dual
  ) t
where n (+) = n+1

ORA-01416：两个表不能相互外连接

：）

Answer 3

我在Oracle 12G中测试了它，它返回的结果与：

相同

SELECT 
   * 
FROM
   TBL_TEST t
WHERE
   t.FIELD = 2;

我对原始代码的猜测是试图说明字段是否等于2，返回字段值，否则返回null。如下所示：

SELECT T.STUDENT, T2.*
  FROM TBL_TEST T
       LEFT OUTER JOIN (SELECT 2 COLU FROM DUAL) T2 ON T.COUNT = T2.COLU;

Oracle（+）运算符数相等

3 个答案: