oracleÖÐselect 1ºÍselect *µÄÇø±ð

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create table myt(name varchar2,create_time date)
 insert into myt values('john',to_date(sysdate,'DD-MON-YY'));
 insert into myt values('tom',to_date(sysdate,'DD-MON-YY'));
 insert into myt values('lili',to_date(sysdate,'DD-MON-YY'));  
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SQL> select * from myt;
 
NAME       CREATE_TIME
---------- -----------
john       2010-5-19
tom        2010-5-19
lili       2010-5-19
 
SQL> select 1 from myt;
 
         1
----------
         1
         1
         1
SQL> select 0 from myt;
 
         0
----------
         0
         0
         0
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¶øselect * from tableÔò·µ»ØËùÓÐÐжÔÓ¦µÄËùÓÐÁС£
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Èçselect * from T1 where exists(select 1 from T2 where T1.a=T2.a) ;
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SQL> select 1/0 from dual;
 
select 1/0 from dual
 
ORA-01476: ³ýÊýΪ 0
SQL> select * from myt where  exists(select 1/0 from dual);
 
NAME       CREATE_TIME
---------- -----------
john       2010-5-19
tom        2010-5-19
lili &nbs