SQL Exercise: Find the floor with the most rooms available

SQL hospital Database: Exercise-26 with Solution

26. From the following tables, write a SQL query to find the floor where the maximum number of rooms are available. Return floor ID as "Floor", count "Number of available rooms".

Sample table: room

Sample Solution:

-- This SQL query retrieves the count of available rooms grouped by blockfloor, where the count of available rooms for each blockfloor is equal to the highest total count of available rooms across all blockfloors.

SELECT blockfloor as "Floor", -- Selects the blockfloor column and aliases it as "Floor"
count(*) AS  "Number of available rooms" -- Counts the number of available rooms for each blockfloor and aliases the result column as "Number of available rooms"
FROM room -- Specifies the table from which to retrieve data, in this case, the room table
WHERE unavailable='false' -- Filters the rows to include only those where the 'unavailable' column is set to 'false'
GROUP BY blockfloor -- Groups the results by blockfloor
HAVING count(*) = -- Filters the groups to include only those where the count of available rooms is equal to the highest total count of available rooms across all blockfloors
  (SELECT max(zz) AS highest_total -- Subquery: Calculates the highest total count of available rooms across all blockfloors
   FROM
( SELECT blockfloor , -- Subquery: Selects the blockfloor column
count(*) AS zz -- Subquery: Counts the number of available rooms for each blockfloor and aliases it as 'zz'
      FROM room -- Subquery: Specifies the table from which to retrieve data, in this case, the room table
      WHERE unavailable='false' -- Subquery: Filters the rows to include only those where the 'unavailable' column is set to 'false'
      GROUP BY blockfloor ) AS t ); -- Subquery: Groups the results by blockfloor and aliases the result set as 't'
  

Sample Output:

 Floor | Number of available rooms
-------+-----------------------
     1 |                     8
(1 row)

Explanation:

The given query in SQL that retrieves the floor and number of available rooms for each floor where rooms are available, groups the results by floor, and then returns only the floor(s) with the highest number of available rooms.

The WHERE clause filters the rows in the room table where the unavailable column is equal to 'false', indicating that the room is available.

The GROUP BY clause groups the rows by the blockfloor column, so that the count function is applied to each distinct floor.

The HAVING clause compares the count of available rooms on each floor to the highest_total value returned by the subquery. Only the floors with the same count as the highest_total are returned.

The subquery calculates the number of available rooms on each floor, and groups them by floor.

The MAX function in the outer query selects the highest number of available rooms across all floors.

Practice Online

E R Diagram of Hospital Database:

Have another way to solve this solution? Contribute your code (and comments) through Disqus.

Previous SQL Exercise: Count unoccupied rooms in each block and floor.
Next SQL Exercise: Find the floor with the minimum available rooms.