Generate rows with time intervals between 2 dates in Oracle - sql

Question

I have table in which Sunday to Saturdy "Doctor Start" and "End Time" is given.
I want to create time slots of 15 minutes.
On the basis of that, the patient clicks on calendar datetime interval which shows slots that have already been booked.

Answer 1

The following example shows how to split time into slices of 15 minutes. It uses hierarchical query. A little bit of explanation:
line 2: trunc function, applied to a date value, returns "beginning" of that day (at midnight). Adding 15 / (24*60) adds 15 minutes (as there are 24 hours in a day and 60 minutes in an hour). Multiplying 15 by level works as a "loop", i.e. adds 15-by-15-by-15 ... minutes to previous value.
line 4: similar to line 2, but it makes sure that a day (24 hours * 60 minutes) is divided to 15-minutes parts
line 6: start time is trivial
line 7: end time just adds 15 minutes to start_time
line 9: return only time between 10 and 16 hours (you don't have patients at 02:15 AM, right?)
SQL> with fifteen as
2 (select trunc(sysdate) + (level * 15)/(24*60) c_time
3 from dual
4 connect by level <= (24*60) / 15
5 )
6 select to_char(c_time, 'hh24:mi') start_time,
7 to_char(c_time + 15 / (24 * 60), 'hh24:mi') end_time
8 from fifteen
9 where extract(hour from cast (c_time as timestamp)) between 10 and 15;
START_TIME END_TIME
---------- ----------
10:00 10:15
10:15 10:30
10:30 10:45
10:45 11:00
11:00 11:15
11:15 11:30
11:30 11:45
11:45 12:00
12:00 12:15
12:15 12:30
12:30 12:45
12:45 13:00
13:00 13:15
13:15 13:30
13:30 13:45
13:45 14:00
14:00 14:15
14:15 14:30
14:30 14:45
14:45 15:00
15:00 15:15
15:15 15:30
15:30 15:45
15:45 16:00
24 rows selected.
SQL>