Using Documentation Effectively 5-12-2004

Question

I am new to Oracle and desperately trying to familiarize myself with the online documentation. I’m having difficulty understanding the sort logic being applied to the following query. My intent is to sort the output by the day of the week on which the employee was hired (Monday, Tuesday, etc.). I found the solution for this problem in my Oracle student manual solutions appendix, but could not find information in my manual or the online documentation explaining why hire_date -1, ‘d’ is needed to order the output in the desired order. Ordering by hire_date, ‘Day’ groups the days together put does not order the days in the desired order. I’m also having problems using -- for commenting certain single lines within my query, and need to use /*…*/ to avoid getting Command beginning "order by t..." is not available in iSQL*Plus errors. Any feedback explaining the intricacies of what is occurring or how I can more effectively find this information in the online documentation is appreciated. – Devin Dowell
column "hire_date - 1, 'd'" format a15
select last_name, hire_date, to_char(hire_date, 'Day') as "DAY", to_char(hire_date - 1, 'd') as "hire_date - 1, 'd'"
from employees
/*order by to_char(hire_date, 'Day');*/
order by to_char(hire_date - 1, 'd');

Answer 1

Devin,
Here's what is happening: the to_char function changes the hire_date to a different format. The format 'Day' yields the day of week as you would see on a calendar; Sunday, Monday, etc. The format 'd' yields the day of week as 1,2,3,4,5,6,or 7. So, ordering by number gives a proper order, while ordering by the other column gives the order Friday, Monday, Tuesday, Thursday, Saturday, Sunday--an alphabetical ordering of the days.
I use Oracle 8i and go here
http://download-east.oracle.com/docs/cd/A87860_01/doc/index.htm
for my documentation. To answer your question from there, I would go to Oracle 8i SQL reference, look for TO_CHAR (date conversion) in Chapter 4 Functions (or look in the index for to_char). This lead me to a link for Format models and then to Table 2-9 Datetime Format Elements.
Hope this helps.