Making problems for myself

Playing around with my toy database I asked myself, "What happens if DUAL has more than 1 row?" I found out.

SQL> insert into dual values ('Y');

1 row created.

SQL> select * from dual;

D
-
X

SQL> select count(*) from dual;

COUNT(*) ---------- 1

I tried it again. Same result. "Oh, I guess I can't insert into DUAL", says I, and I went about my business.

Later I logged on as SCOTT and tried to drop a table. Playing I have more EMP tables than employees.

SQL> DROP TABLE EMP4;

ERROR at line 1:

ORA-00604: error occurred at recursive SQL level 1

ORA-01422: exact fetch returns more than requested number of rows

WHAT??!!?

Yes it is there and there is only 1 table called EMP4.

SELECT OWNER, OBJECT_NAME FROM ALL_OBJECTS WHERE OBJECT_NAME = 'EMP4'

OWNER OBJECT_NAME

------------------------------ ------------------------------

SCOTT EMP4

I looked the matter up at orafaq. and followed the instructions.

SQL> select * from dual;

D

-

X

SQL> create table temp_dual as select * from dual;

Table created.

SQL> select * from temp_dual;

D

-

X

Y

Y

Yes, I plead guilty. I DID succeed in inserting those rows into DUAL.

SQL> delete from dual where dummy = 'Y';

1 row deleted.

Strange. It deleted 1 row even though I had put 2 in.

SQL> drop table temp_dual;

drop table temp_dual

*

ERROR at line 1:

ORA-00604: error occurred at recursive SQL level 1

ORA-01422: exact fetch returns more than requested number of rows

I deleted the second excess row:

SQL> delete from dual where dummy = 'Y';

1 row deleted.

and I had a functioning database back.

SQL> DROP TABLE TMP_DUAL;

Table dropped.

and then as SCOTT

SQL> DROP TABLE EMP4;

Table dropped.

OK, I get it, Oracle consults DUAL in the drop process. And don't go messing up a database of any importance. But it is odd how the fact that I was succeeding to mess things up was hidden from me. Yes it told me that I had inserted the row, but then it didn't display it with a select. It was an interesting bit of play.