Adding a column makes big difference with a simple query

Question

Hello All,
The oracle environment I am working with is
Oracle9i Enterprise Edition Release 9.2.0.8.0 - 64bit Production
and
PL/SQL Release 9.2.0.8.0 - Production
I have a question for the following 2 queries. The only difference is that first one has an extra field than the second one. That extra field makes big difference regarding excution time. One is 4 seconds and the other is 5 minutes. Could anyone help me to understand why? Thank you for your help! -Susan
4 Seconds
================================================================
select distinct B.A_CA.CA_ID, B.A_CA.CE_ID
from B.A_CA, B.CA_LIST_DTLS
where UPPER(deleted(B.A_CA.CA_ID) = 'N'
and UPPER(B.CA_LIST_DTLS.CA_LIST_NAME) = 'SW'
and B.A_CA.CA_ID = B.CA_LIST_DTLS.CA_ID ;
5 minutes
==============================================================
select distinct B.A_CA.CA_ID
from B.A_CA, B.CA_LIST_DTLS
where UPPER(deleted(B.A_CA.CA_ID) = 'N'
and UPPER(B.CA_LIST_DTLS.CA_LIST_NAME) = 'SW'
and B.A_CA.CA_ID = B.CA_LIST_DTLS.CA_ID ;
Below is the function
=============================================================
FUNCTION deleted ( in_ca_id IN B.A_CA.CA_ID%TYPE ) RETURN VARCHAR2 IS
n_result VARCHAR2(20);
cnt NUMBER :=0;
cursor cur is
SELECT COUNT(*)
from B.A_CA
where B.A_CA.CA_ID=in_ca_id
and (B.A_CA.COMPLAINT_FLAG = 'Y'
or B.A_CA.DELETE_FLAG = 'Y') ;
BEGIN
OPEN cur;
FETCH cur INTO cnt;
CLOSE cur;
If cnt >0 then
n_result := 'Y';
else
n_result := 'N';
end if;
RETURN n_result;
EXCEPTION
WHEN NO_DATA_FOUND THEN
return 'N/A';
END;
Edited by: 849989 on Apr 5, 2011 10:25 AM

Answer 1

Explain plan for two queries:
The fast one:
Plan
SELECT STATEMENT CHOOSE Cost: 4,223 Bytes: 116,032 Cardinality: 2,072
5 SORT UNIQUE Cost: 4,223 Bytes: 116,032 Cardinality: 2,072
4 NESTED LOOPS Cost: 4,212 Bytes: 116,032 Cardinality: 2,072
1 TABLE ACCESS FULL B.CA_LIST_DTLS Cost: 68 Bytes: 87,024 Cardinality: 2,072
3 TABLE ACCESS BY INDEX ROWID B.A_CA Cost: 2 Bytes: 14 Cardinality: 1
2 INDEX UNIQUE SCAN UNIQUE B.A_CA_PK Cost: 1 Cardinality: 1
The slow one:
Plan
SELECT STATEMENT CHOOSE Cost: 305 Bytes: 111,888 Cardinality: 2,072
4 SORT UNIQUE Cost: 305 Bytes: 111,888 Cardinality: 2,072
3 HASH JOIN Cost: 295 Bytes: 111,888 Cardinality: 2,072
1 TABLE ACCESS FULL B.CA_LIST_DTLS Cost: 68 Bytes: 87,024 Cardinality: 2,072
2 INDEX FAST FULL SCAN UNIQUE B.A_CA_PK Cost: 225 Bytes: 131,928 Cardinality: 10,994
Edited by: 849989 on Apr 5, 2011 11:49 AM