mysql - error : #1242 - Subquery returns more than 1 row

Question

I got an error: #1242 - Subquery returns more than 1 row when i run this sql.

CREATE VIEW test 
AS 
  SELECT cc_name, 
         COUNT() AS total, 
         (SELECT COUNT(*) 
            FROM bed 
           WHERE respatient_id > 0 
        GROUP BY cc_name) AS occupied_beds, 
         (SELECT COUNT(*) 
            FROM bed 
           WHERE respatient_id IS NULL 
        GROUP BY cc_name) AS free_beds 
    FROM bed 
GROUP BY cc_name; 

Answer 1

The problem is that your subselects are returning more than one value - IE:

SELECT ...
       (SELECT COUNT(*) 
          FROM bed 
         WHERE respatient_id IS NULL 
      GROUP BY cc_name) AS free_beds,
       ...

...will return a row for each cc_name, but SQL doesn't support compacting the resultset for the subselect - hence the error.

Don't need the subselects, this can be done using a single pass over the table using:

  SELECT b.cc_name, 
         COUNT(*) AS total, 
         SUM(CASE 
               WHEN b.respatient_id > 0 THEN 1 
               ELSE 0 
             END) AS occupied_beds, 
         SUM(CASE 
               WHEN b.respatient_id IS NULL THEN 1 
               ELSE 0 
             END) AS free_beds 
    FROM bed b
GROUP BY b.cc_name