MySQL timestamp modification, addition, and comparison

Question

I am creating a view that involves a little bit of fiddling with timestamps.

I have a table A with timestamps. The view will process the timestamps to see if each timestamp is within a certain range (9 AM - 5 PM). If the timestamp is within that range, I will fetch data matching the exact time in another table (B). Otherwise, I will fetch the next day (or this day's) first valid time (which is 9 AM) and the corresponding data from there.

Examples:

• A record with timestamp of 12/28/2012 17:01 -> fetch data from B for 12/29/2012 09:00 , set flag to after .
• A record with timestamp of 12/28/2012 08:59 -> fetch data from B for 12/28/2012 09:00 , set flag to before .
• A record with timestamp of 12/28/2012 09:55 -> fetch data from B for 12/28/2012 09:55 , set flag to null .

Here is what I have so far (not working, some in pseudocode). I mainly don't know how to set the flag based on the comparison and then, based on flag, perform next operation on b - all in one statement.

CREATE VIEW C as 
SELECT time, (CASE WHEN (time< '9:00' ) THEN'before'
CASE WHEN(time> '17:00') THEN'after' else null END) AS flag FROM A

//These two should be combined into one create view statement
//The below is utterly wrong, I know, but explains what I mean
SELECT(
CASE WHEN (flag=='before') THEN SELECT * FROM B WHERE B.time = time set hour='9:00'
CASE WHEN(flag=='after') THEN SELECT* FROM B WHERE B.time = time + one day set hour='9:00'
ELSE SELECT* FROM B WHERE B.time = time ) as data

Answer 1

Tested using this fiddle: http://sqlfiddle.com/#!2/15be5/50

SELECT
  q.time as original_time_check,
  q.flag as flag_check,
  case q.flag
    when 'before' then q.NINE_AM_ON_THE_DAY 
    when 'after' then q.NINE_AM_THE_NEXT_DAY 
    else q.time
  end as time


FROM
(
    SELECT
       time,
       date(time) + INTERVAL 9 HOUR as NINE_AM_ON_THE_DAY,
       date(time) + INTERVAL '1 9' DAY_HOUR as NINE_AM_THE_NEXT_DAY,  
       case
         when time < (date(time) + INTERVAL 9 HOUR) then 'before'
         when time < (date(time) + INTERVAL 17 HOUR) then 'in-range'
         else 'after'
       end as flag
    FROM 
       Your_table 
) q