﻿ SQL: Count the number available rooms

# SQL Exercise: Count the number available rooms

## SQL hospital Database: Exercise-6 with Solution

6. From the following table, write a SQL query to count the number available rooms. Return count as "Number of available rooms".

Sample table: room

Sample Solution:

``````SELECT count(*) "Number of available rooms"
FROM room
WHERE unavailable='false';
``````

Sample Output:

``` Number of available rooms
---------------------------
29
(1 row)
```

Explanation:

The said query here in SQL that counts the number of available rooms in the room table.

The query selects all columns (*) from the room table where the unavailable column is set to 'false'.

The resulting output is a single row with a single column, showing the number of available rooms in the room table. The column will be labeled "Number of available rooms".

Pictorial presentation:

## Practice Online

E R Diagram of Hospital Database:

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Previous SQL Exercise: Find the floor and block with a given room number.
Next SQL Exercise: Count the number of unavailable rooms.

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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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