ORA-00937: not a single-group group function

Question

SELECT MIN(retail)
FROM books
WHERE category = 'COMPUTER'

works fine, but when I include title in select like:

SELECT MIN(retail), title
FROM books
WHERE category = 'COMPUTER'

it doesn't. Why? How to make it work?

Answer 1

Rhys's answer is correct, if that is what you mean, but you might have wanted the title(s) where retail=MIN(retail), and that wording suggests how to get that answer:

SELECT title, retail
FROM books
WHERE category = 'COMPUTER'
 AND retail = (SELECT MIN(retail) FROM books WHERE category = 'COMPUTER')

To reduce duplication you can use a WITH clause (if you're using a recent version of SQL):

;WITH ComputerBooks AS (
  SELECT title, retail
  FROM books
  WHERE category = 'COMPUTER')
SELECT title, retail
FROM ComputerBooks
WHERE retail = (SELECT MIN(retail) FROM ComputerBooks)

Sample I used to confirm syntax.

Answer 2

MIN applies to a group of records, so you need to tell it which group of records you mean.

If you mean for each title, show the minimum of retail, then you need:

SELECT MIN(retail), title FROM books
WHERE category = 'COMPUTER'
GROUP BY title