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Databases

Posted by Laurence kite
Laurence kite
11,768 Points

Querying SQL by Andrew Chalkey (sql playground exercise)

I wanted to see if this is a correct solution to the sql playground exercise for the subqueries This is the link to the playground questions.

https://teamtreehouse.com/sql_playgrounds/522#/queries/0cb93e9a-58f8-45d7-bb22-b15a6cf94d35 Exercise 2

  • Generate a report that lists a patron's first name, email and loan count for loans that haven't been returned

My solution : 

SELECT  first_name, email, COUNT(email) AS "Loan Count"  FROM patrons AS P
 INNER JOIN (SELECT * FROM loans_south UNION ALL SELECT * FROM loans_north) AS allLoans
  ON P.id = allLoans.patron_id
  WHERE returned_on IS NULL
  GROUP BY email;

Also is there an easier or better solution i am sure there lol

1 Answer

Steven Parker
Steven Parker
229,744 Points
Steven Parker
Steven Parker
229,744 Points

I think you essentially have it. :+1: But other DB's might not let you get away with including a non-aggregate in the output without naming it in the GROUP BY. And you could could optionally limit the subquery to just the fields you need:

SELECT first_name, email, COUNT(email) AS "Loan Count"
FROM patrons AS P
INNER JOIN (SELECT patron_id, returned_on FROM loans_south
            UNION ALL
            SELECT patron_id, returned_on FROM loans_north) AS allLoans
      ON P.id = allLoans.patron_id
WHERE returned_on IS NULL
GROUP BY first_name, email;
Laurence kite
Laurence kite
11,768 Points

Cheers for your help...!