I created a table with two columns, and the second column is a virtual column and contains a constant. I created a unique index on this column. On every insertion, this second column always evaluates to 1, and unique index (which become the function based index on virtual column) ensures that only one row remains in the table.
oracle@test # sqlplus /nolog
SQL*Plus: Release 11.1.0.7.0 - Production on Sat Aug 28 19:09:16 2010
Copyright (c) 1982, 2008, Oracle. All rights reserved.
idle> conn test/test
Connected.
test@test> create table t1 (c1 number, c2 generated always as (1) virtual);
Table created.
test@test> create unique index idx1 on t1(c2);
Index created.
test@test> insert into t1(c1) values (1);
1 row created.
test@test> commit;
Commit complete.
test@test> insert into t1(c1) values (1);
insert into t1(c1) values (1)
*
ERROR at line 1:
ORA-00001: unique constraint (TEST.IDX1) violated
test@test> insert into t1(c1) values (2);
insert into t1(c1) values (2)
*
ERROR at line 1:
ORA-00001: unique constraint (TEST.IDX1) violated
1 comment:
hello Fahd,
I would suggest this :
Connected to
Connected as SYS
SQL> create table Onerow(a number);
Table created
SQL> insert into onerow values(1);
1 row inserted
SQL> commit;
Commit complete
SQL> alter table onerow read only;
Table altered
SQL> insert into onerow values(2);
insert into onerow values(2)
ORA-12081: no se permite la operación de actualización en la tabla "SYS"."ONEROW"
SQL>
Thaksn,
Wissem EL KHLIFI
http://oracle-tns.com/
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