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SQL Exercise: Count the number of rooms in each block on each floor

SQL hospital Database: Exercise-24 with Solution

24. From the following tables, write a SQL query to count the number of available rooms for each floor in each block. Sort the result-set on floor ID, ID of the block. Return the floor ID as "Floor", ID of the block as "Block", and number of available rooms as "Number of available rooms".

Sample table: room


Sample Solution:

SELECT blockfloor AS "Floor",
       blockcode AS "Block",
       count(*) "Number of available rooms"
FROM room
WHERE unavailable='false'
GROUP BY blockfloor,
        blockcode
ORDER BY blockfloor,
        blockcode;

Sample Output:

 Floor | Block | Number of available rooms
-------+-------+---------------------------
     1 |     1 |                         3
     1 |     2 |                         2
     1 |     3 |                         3
     2 |     1 |                         2
     2 |     2 |                         2
     2 |     3 |                         3
     3 |     1 |                         2
     3 |     2 |                         3
     3 |     3 |                         2
     4 |     1 |                         2
     4 |     2 |                         3
     4 |     3 |                         2
(12 rows)

Explanation:

The said query in SQL that selects the blockfloor and blockcode columns and counts the number of available rooms by grouping the data by blockfloor and blockcode where the value of unavailable column is 'false'.

The WHERE clause filters the data by only selecting rows where the value of the unavailable column is 'false'.

The GROUP BY clause groups the data by blockfloor and blockcode, which allows the count of available rooms to be aggregated by these columns.

The ORDER BY clause orders the results by blockfloor and blockcode in ascending order.

Practice Online


E R Diagram of Hospital Database:

E R Diagram: SQL Hospital Database.

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Previous SQL Exercise: Count the number of available rooms in each floor.
Next SQL Exercise: Count unoccupied rooms in each block and floor.

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SQL: Tips of the Day

Grouped LIMIT in PostgreSQL: Show the first N rows for each group?

db=# SELECT * FROM xxx;
 id | section_id | name
----+------------+------
  1 |          1 | A
  2 |          1 | B
  3 |          1 | C
  4 |          1 | D
  5 |          2 | E
  6 |          2 | F
  7 |          3 | G
  8 |          2 | H
(8 rows)

I need the first 2 rows (ordered by name) for each section_id, i.e. a result similar to:

id | section_id | name
----+------------+------
  1 |          1 | A
  2 |          1 | B
  5 |          2 | E
  6 |          2 | F
  7 |          3 | G
(5 rows)

PostgreSQL v9.3 you can do a lateral join

select distinct t_outer.section_id, t_top.id, t_top.name from t t_outer
join lateral (
    select * from t t_inner
    where t_inner.section_id = t_outer.section_id
    order by t_inner.name
    limit 2
) t_top on true
order by t_outer.section_id;

Database: PostgreSQL

Ref: https://bit.ly/3AfYwZI

 





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