DELETE FROM Subquery Question

Question

When having to delete form a subquery (based on two unique identifiers) I concantenate the two columns to make them unique to an entry. Are there issues w/ this method and can any suggest something different (if any).
delete from ACCT_TEMP a where upper(a.id_name) || a.system_id in (
select upper(a.id_name) || a.system_id from ACCT_TEMP a, ACCT b
where upper(trim(both ' ' from a.id_name)) = upper(trim(both ' ' from b.account_name)) and a.system_id = b.system_id)

Answer 1

Topher34 wrote:
I had this problem before. Because, say I have an ID ABC123 on System 12345. And, the ABC123 also existed on system 98765. That is the reason I concant.
But, when I did the delete from table where (col1, col2) in (select blahblahblahblah) it would delete the entire table. I played w/ it forever and forever!You need to be careful when using uncorrelated subqueries like the ones used with the IN operator. If you're accidentally referring to columns from the outer query, they will get used without warning which can lead to such side effects, since you effectively say e.g. "from table_1 where (col1, col2) in (select col1, col2 from table_2)", but in table_2 there is no "col1" or "col2", see the following small example:
SQL> create table test_1 as
  2  select 1 as col1, 2 as col2
  3  from dual;
Table created.
SQL> create table test_2 as
  2  select 3 as col3, 4 as col4
  3  from dual;
Table created.
SQL> desc test_1
Name                                      Null?    Type
COL1                                               NUMBER
COL2                                               NUMBER
SQL> desc test_2
Name                                      Null?    Type
COL3                                               NUMBER
COL4                                               NUMBER
SQL> delete from test_1
  2  where (col1, col2) in (
  3    select col1, col2
  4    from test_2
  5  );
1 row deleted.
SQL> rollback;Regards,
Randolf
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