SQL> select * from v$version;
BANNER
---------------------------------------------
Oracle9i Enterprise Edition Release 9.0.1.1.1
PL/SQL Release 9.0.1.1.1 - Production
CORE 9.0.1.1.1 Production
TNS for 32-bit Windows: Version 9.0.1.1.0 - P
NLSRTL Version 9.0.1.1.1 - Production
SQL> set null NULL
SQL> select a.aaa,b.bbb from
2 (select 1 as aaa from dual) a
3 left join (select 1 as bbb from dual
4 union select 2 from dual
5 union select 3 from dual) b
6 on a.aaa=b.bbb and b.bbb=2;
AAA BBB
--- ----
1 NULL
SQL> select a.aaa,b.bbb from
2 (select 1 as aaa from dual) a
3 left join (select 1 as bbb from dual
4 union select 2 from dual
5 union select 3 from dual) b
6 on a.aaa=b.bbb and 2=b.bbb;
AAA BBB
--- ---
1 1
Why different?