如何计算小时之间的total_number-MySQL

Question

I have a Mysql table like

|Doctor_id | login_hour | logout_hour |
-------   -----------  -----------
 12         10          12
 13         11          13
 14         09          13
 15         13          14

I want to know how many doctors is schedule for every hour. If the doctor has schedule between 11 and 13, he should appear in 11th & 12th hour.Kindly let me know how to do this in MySQL

The output should be like

Hour | Number_of_doctors
----   -----------------
10         2
11         3
12         2
13         1

Answer 1

You can do with inner SELECT , eg:

SELECT DISTINCT t.login_hour,
(SELECT COUNT(*) FROM doctors WHERE login_hour <= t.login_hour AND logout_hour 
> t.login_hour) AS number_of_doctors
FROM doctors t
ORDER BY t.login_hour;

Here's the SQL Fiddle .

Update

This would assume at least one doctor is logged in (as Strawberry has rightly said). If you want the total number of doctors logged in at any given hour then you can use the below query:

SELECT COUNT(*) 
FROM doctors WHERE login_hour <= ? AND logout_hour > ?;

Answer 2

Here's one idea - but as stated in comments, I'd actually handle the bulk of this in application code...

SELECT x.hour
     , COUNT(*) total
  FROM
     ( SELECT  9 hour UNION 
       SELECT 10 UNION
       SELECT 11 UNION
       SELECT 12 UNION
       SELECT 13 UNION
       SELECT 14 
     ) x
  JOIN my_table y
    ON x.hour >= y.login_hour 
   AND x.hour < y.logout_hour
 GROUP
    BY hour;