distinct返回null报错_ORACLE distinct 问题

我用了如下语句就报错：selectdistinct*fromA_Dtla,B_RTbwherea.MgrGid=b.MgrGidEx报错界面已上传，点下OK就提示未连接到ORACLE，但实际上是连接的，我用了select*fromdual仍能查出数...

我用了如下语句就报错：

select distinct * from A_Dtl a, B_RT b where a.MgrGid = b.MgrGidEx

报错界面已上传，点下OK就提示未连接到ORACLE，但实际上是连接的，我用了select * from dual仍能查出数据，表结构如下：

CREATE TABLE ZH_Performance_Dtl (

AGid Varchar2(32) not null,

CreateDate Date Default sysdate not null,

LastupdDate Date Default sysdate not null,

--

UsrGid Varchar2(32) not null,

UsrCode Varchar2(64) null,

UsrName Varchar2(64) null,

ShopGid Varchar2(32) null,

ShopCode Varchar2(64) null,

ShopName Varchar2(64) null,

AssessDate Date null,

AYear int not null,

AMonth int not null,

Stat int Default 0 not null,

--

MgrGid Varchar2(32) null,

MgrCode Varchar2(64) null,

MgrName Varchar2(64) null,

--

A1 DECIMAL(20,4) NULL,

A2 DECIMAL(20,4) NULL,

A3 DECIMAL(20,4) NULL,

A4 DECIMAL(20,4) NULL,

A5 DECIMAL(20,4) NULL,

A6 DECIMAL(20,4) NULL,

B1 Varchar2(1024) null,

SCORE DECIMAL(20,4) DEFAULT 0 NOT NULL,

Constraint PK_ZH_Performance_Dtl PRIMARY KEY(EntGid, UsrGid, AYear, Amonth, MgrGid)

);

CREATE TABLE ZH_Performance_RT (

AGid Varchar2(32) not null,

UsrGidEx Varchar2(32) not null,

UsrCodeEx Varchar2(64) null,

UsrNameEx Varchar2(64) null,

ShopGidEx Varchar2(32) null,

ShopCodeEx Varchar2(64) null,

ShopNameEx varchar2(64) null,

MgrGidEx Varchar2(32) not null,

MgrCodeEx Varchar2(64) null,

MgrNameEx varchar2(64) null,

Constraint PK_ZH_Performance_RT PRIMARY KEY(EntGid, UsrGidEx, MgrGidEx)

);

麻烦高手指点下，希望试过成功后在说，因为这种用法在我新建的两张表是能用的，这两张表的问题出在哪呢？我用的是10G版本的

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