MySQL change virtual column based on WHERE clause

Is it possible to change a virtual column value based on a where clause?

I have this table:

[computername] [computerlocation]  [starttime]  [endtime]
computer,      siteA,              1457537657,  1457532657
computer2,     siteB,              1457547657,  1457546657
computer3,     siteB,              1457237657,  14575237657

I'd like to see how many computers there are, at a given site and in a given time frame, the query I currently use is:

select count(*), computerlocation 
from table 
where site like "site%" 
  and starttime <= "1457532657" and endtime >= "1457532657" 
group by computerlocation

However, at the moment I have to run this query hundreds of times to create a graph which displays over a period of time how many computers there are.

Is it possible to make something like this:

select count(*), computerlocation, "null" as time 
from table 
where site like "site%" 
 and ( (starttime <= "1457532657" and endtime >= "1457532657" as time="timeA") 
    OR (starttime <= "1457532357" and endtime >= "1457532357" as time="timeB") 
    OR (starttime <= "1457532651" and endtime >= "1457532651" as time="timeC") 
     ) 
group by time, computerlocation

Solution

You use a CASE expresion

First you create your virtual column, and then you perform the group by

SELECT time_group, computerlocation, count(*)
FROM (
        SELECT computerlocation,
                CASE WHEN (starttime <= '1457532657' and endtime >= '1457532657') THEN 'timeA'
                     WHEN (starttime <= '1457532357' and endtime >= '1457532357') THEN 'timeB'
                     WHEN (starttime <= '1457532651' and endtime >= '1457532651') THEN 'timeC'
                     ELSE 'N/A'
                END as time_group
        from table 
        where site like 'site%'
     ) T
GROUP BY time_group, computerlocation

btw double quotes mean "fieldname" single quotes mean string 'string'

You should check BETWEEN comparator, should be write as

WHERE '1457532657' BETWEEN starttime AND endtime