substr Question

[frangac]

Hi All

Is there any explanation as to why the SQL1 statement (substr) takes longer than the SQL2 statement?
They are both index the same.

SQL1
select count(*) from CE.CDR_DRMS
where substr(FE_F,9,8) >= '20041001' and substr(FE_F,9,8) <= '20041001'
and STAT_CODE like 'r%';

SQL2
select count(*) from CE.CDR_DRMS
where R_DT >= '20041001 00:00:00' and R_DT <= '20041001 23:59:59'
and STAT_CODE like 'r%';

Many Thanks
Chris

 

[toring]

SQL1
If there is an index on FE_F it will never be used (function on a column).