How to restrict only one row in Table ??.

Question

Hi all,
i want to restrict no. of rows to one,
that is not more that one row should be there in the table.
Following trigger works well in all conditions
except:
insert into myTab select 'x' from emp;
inserts 14 rows.
Create or replace trigger one_row_myTab
before insert on myTab
for each row
declare
cnt number;
pragma AUTONOMOUS_TRANSACTION;
Begin
select count(*) into cnt from mydual;
if cnt=1 then
raise_application_error(-20001,'MyDual Can have only one Row');
end if;
end;
i think with trigger it w't be possible because,
same transaction triggers c't query the table (Mutating Table),
Autonomus trans ca't identify uncommited changes.
pls add your suggestions.
Thanks for Reading the Post.
Rajashekhar Ganga,
mail : [email protected]

Answer 1

nice try Mulder ! it doesn't work everywhere...
SQL> connect scott/tiger@lsc69
Connected to:
Oracle7 Server Release 7.3.4.5.0 - Production
With the distributed and parallel query options
PL/SQL Release 2.3.4.5.0 - Production
SQL>  create table d as select * from dual;
Table created.
SQL> create index i on d(1);         
create index i on d(1)
ERROR at line 1:
ORA-00904: invalid column name
SQL> connect scott/tiger@lsc65
Connected to:
Oracle8i Enterprise Edition Release 8.1.7.4.0 - 64bit Production
JServer Release 8.1.7.4.0 - 64bit Production
SQL> create table d as select * from dual;
Table created.
SQL> create index i on d(1);         
Index created.
SQL> connect scott/tiger@lsc68
Connected to:
Oracle Database 10g Enterprise Edition Release 10.1.0.3.0 - 64bit Production
With the Partitioning and Data Mining options
SQL> create table d as select * from dual
Table created.
SQL> CREATE UNIQUE INDEX i on d(1);                  
CREATE UNIQUE INDEX i on d(1)
ERROR at line 1:
ORA-03113: end-of-file on communication channel