请问这是ORACLE的Bug吗

先准备数据：

CREATE TABLE Table_A(EID NUMBER PRIMARY KEY);

/

CREATE TABLE Table_B(EID NUMBER PRIMARY KEY,EMail VARCHAR2(300));

/



INSERT INTO Table_A(EID)

SELECT 1 FROM Dual UNION ALL

SELECT 2 FROM Dual UNION ALL

SELECT 3 FROM Dual UNION ALL

SELECT 4 FROM Dual;

/

INSERT INTO Table_B(EID,Email)

SELECT 3,'123@qq.com' FROM Dual UNION ALL

SELECT 4,'234@qq.com' FROM Dual;

/

COMMIT;

再看查询：

--有返回记录

SELECT a.EID

FROM Table_A a

LEFT JOIN Table_B b ON a.EID = b.EID;



-- 无返回记录？？？

SELECT a.EID

FROM Table_A a

LEFT JOIN (SELECT EID,EMail FROM Table_B WHERE EID IN (3,4)) b ON a.EID = b.EID;



-- 加一列，又返回记录了!!!

SELECT a.EID,b.Email

FROM Table_A a

LEFT JOIN (SELECT EID,EMail FROM Table_B WHERE EID IN (3,4)) b ON a.EID = b.EID;



-- 用COUNT(*)包一层，结果居然是0

SELECT COUNT(*)

FROM (SELECT a.EID,b.Email

FROM Table_A a

LEFT JOIN (SELECT EID,EMail FROM Table_B WHERE EID IN (3,4)) b ON a.EID = b.EID);

奇怪的是，上面建表时，如果不加主键，则上面第2个查询是有记录的，最后一个也不是返回0.

附ORACLE版本：

Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production
PL/SQL Release 11.2.0.1.0 - Production
CORE 11.2.0.1.0 Production
TNS for 32-bit Windows: Version 11.2.0.1.0 - Production
NLSRTL Version 11.2.0.1.0 - Production