Oracle Database Discussions

Hi,

I'm during preparing test on select statement to check what clause cause the most slow down. Therefore I prepare 3 select statement:
1) select which transform all columns in source table for oracle's functions like: substr, rpad, decode, nvl,upper, mod, greatest, length, power, instr etc..
2) select with big where clause (about 7 lines) which take from 2 tables
3) select which have where, group by, having and order by clauses
Perhaps I will have first result today. But I am very interested what is your experience in this subject?? Which case cause the biggest slow down?

Best.