SQL query about appointments

Suppose we have this table..

CREATE TABLE `appointments` (
  `idappointments` int(11) NOT NULL AUTO_INCREMENT,
  `timeStart` time DEFAULT NULL,
  `timeEnd` time DEFAULT NULL,
  PRIMARY KEY (`idappointments`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8$$

assumption

Suppose that a range between timeStart and timeEnd cant exist again... I mean that if we intersect all the ranges in the table the result would be EMPTY ,0 , null.An appointment cant cooexist with another..

So what i want to do is a time suggestion if the desired time is occupied... A proposal before and a proposal after the desired time....

So i was wondering instead of writing code to do this if i could write an SQL query to find the nearest empty ranges......

Ex.. timeStart - NEAREST_TO_TIMESTART_TIMEEND >'10 minutes' whereas 10 minutes the duration

Solution

MySQL doesn't have recursive functionality, so you're left with using the NUMBERS table trick -

Create a table that only holds incrementing numbers - easy to do using an auto_increment:

DROP TABLE IF EXISTS `example`.`numbers`;
CREATE TABLE  `example`.`numbers` (
  `id` int(10) unsigned NOT NULL auto_increment,
   PRIMARY KEY  (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

Populate the table using:
```
INSERT INTO NUMBERS
  (id)
VALUES
  (NULL)
```
...for as many values as you need.
Use DATE_ADD to construct a list of dates, increasing the days based on the NUMBERS.id value. Replace "2010-01-01" and "2010-01-02" with your respective start and end dates (but use the same format, YYYY-MM-DD HH:MM:SS) -
```
SELECT x.dt
  FROM (SELECT TIME(DATE_ADD('2010-01-01', INTERVAL (n.id - 1) * 15 MINUTE)) AS dt
          FROM numbers n
         WHERE DATE_ADD('2010-01-01', INTERVAL (n.id - 1) * 15 MINUTE) <= '2010-01-02' ) x
```
LEFT JOIN onto your table of data based on the datetime portion.

This will show you the first available slot:

       SELECT x.dt
      FROM (SELECT TIME(DATE_ADD('2010-01-01', INTERVAL (n.id - 1) * 15 MINUTE)) AS dt
              FROM numbers n
             WHERE DATE_ADD('2010-01-01', INTERVAL (n.id - 1) * 15 MINUTE) <= '2010-01-02' ) x
    LEFT JOIN APPOINTMENTS a ON x.dt BETWEEN a.timestart AND a.timeend
        WHERE a.idappoinment IS NULL
          AND x.dt > @your_minimum_datetime
     ORDER BY x.dt
        LIMIT 1

This will show you availability for the entire day:

       SELECT x.dt,
              CASE 
                WHEN a.idappoinment IS NULL THEN 'available'
                ELSE 'booked'
              END AS isbooked 
      FROM (SELECT TIME(DATE_ADD('2010-01-01', INTERVAL (n.id - 1) * 15 MINUTE)) AS dt
              FROM numbers n
             WHERE DATE_ADD('2010-01-01', INTERVAL (n.id - 1) * 15 MINUTE) <= '2010-01-02' ) x
    LEFT JOIN APPOINTMENTS a ON x.dt BETWEEN a.timestart AND a.timeend
     ORDER BY x.dt

Why Numbers, not Dates?

Simple - dates can be generated based on the number, like in the example I provided. It also means using a single table, vs say one per data type.