SQL JOINING TABLE QUERY

Question

I have to give a count of the number of rooms in the Sparrow wing. I have a table for WING and a table for BEDROOMS . The bedroom table has wing_id as a foreign key and I'm having trouble joining the tables.

This is the query I have tried so far-

SELECT BEDROOM_ID, COUNT(*) 
FROM BEDROOMS 
WHERE WING_ID =
(
    SELECT WING_NAME
    FROM WING
    WHERE WING_NAME='SPARROW'
)
GROUP BY WING_NAME;

getting an error - not a GROUP BY expression. Does anybody know how I can make this work?

Answer 1

This should give you the number of bedrooms in the SPARROW wing:

SELECT COUNT(*) 
  FROM BEDROOMS   B,
       WING       W
 WHERE W.WING_NAME = 'SPARROW'
   AND B.WING_ID = W.WING_ID;

From what you're asking, you don't seem to need a group by. The reason, however, you're getting the error, is you're trying to select "BEDROOM_ID", however, BEDROOM_ID isn't in your GROUP BY clause.

Answer 2

You can't use BEDROOM_ID in the SELECT clause if it's not in the GROUP BY clause. further more, This query will not work since you are comparing WING_ID with WING NAME. Also, I don't think you even need to use GROUP BY for this count.

SELECT 'SPARROW', COUNT(BEDROOM_ID) 
FROM BEDROOMS INNER JOIN WING
ON(BEDROOMS.WING_ID = WING.WING_ID)
WHERE WING_NAME='SPARROW'

Answer 3

Before writing a query, think about what you want to select and show. You are telling us that you want to count bedrooms in the Sparrow wing. So why do you select bedroom_id in your query? Which bedroom ID would you show of all those bedrooms in the wing?

Then you select from bedrooms where the wing ID is the one in question. But in the subquery you don't select the wing ID, but the wing name (which is 'SPARROW' of course). I suppose that is just a typo, right?

Then you group by wing_name. Thus you get one record per wing name. But you are only selecting records for one wing (SPARROW), so the GROUP BY clause doesn't do anything helpful. Moreover you are using it in the bedroom query, but the bedrooms table doesn't have a column wing_name, so you cannot group by it anyhow.

Here is your query cleaned up:

select count(*) 
from bedrooms 
where wing_id =
(
  select wing_id
  from wing
  where wing_name = 'SPARROW'
);

You can also select min(bedroom_id), max(bedroom_id), the literal 'SPARROW', etc.

If you want to select columns from table wing, too, then select from wing and use a sub-query on bedrooms:

select 
  wing_name, 
  wing_size,
  (select count(*) from bedrooms b where b.wing_id = w.wing_id) as rooms
from wing w 
where wing_name = 'SPARROW';

Answer 4

Try This:

SELECT W.WING_NAME AS WING,COUNT(B.WING_ID) AS BED
 FROM WING W JOIN BEDROOM B
  ON W.WING_ID=B.WING_ID
GROUP BY B.WING_ID;