Operand should contain 1 column(s) error

Question

I have an sql query that was returning some incorrect results due to product id's being duplicated for linked products, so i added the following to the end of my query expecting it to only take the first instance of any product id:

AND pc.products_id 
IN
(SELECT
pc.products_id, MIN(categories_id)
FROM
zen_products_to_categories pc
GROUP BY
pc.products_id)

But i get an Operand should contain 1 column(s) error when i run the process. I ran that query on it's own and it only gave me each product id once, so not sure why i get the error.

The full query i now have is:

SELECT p.products_quantity, p.abebooks_status, 
p.products_id AS id, 
p.products_status AS prodStatus, 
FORMAT( IFNULL(s.specials_new_products_price, p.products_price),2) AS price, 
pc.categories_id AS prodCatID, 
c.parent_id AS catParentID, 
cd.categories_name AS catName 
FROM 
zen_products p 
JOIN zen_products_description pd ON p.products_id=pd.products_id 
JOIN zen_products_to_categories pc ON p.products_id=pc.products_id 
JOIN zen_categories c ON pc.categories_id=c.categories_id 
JOIN zen_categories_description cd ON c.categories_id=cd.categories_id 
left join zen_specials s on ( s.products_id = p.products_id AND ( (s.expires_date > CURRENT_DATE) OR (s.expires_date = 0) ) ) 
WHERE p.products_price > 0 and p.products_status = 1 
AND pc.products_id 
IN 
(SELECT pc.products_id, MIN(categories_id) 
FROM zen_products_to_categories pc GROUP BY pc.products_id) 
ORDER BY catName ASC 

Can anyone tell me why it doesn't work when i add the extra query because it's got me baffled

Answer 1

You could try with:

AND (pc.products_id, pc.categories_id) 
    IN
    (SELECT
       pc.products_id, MIN(categories_id)
     FROM
       zen_products_to_categories pc
     GROUP BY
       pc.products_id)

Edit:

In MySQL a subquery like this is usually slow. You should have better luck with a JOIN:

SELECT ....
FROM
  ....
  INNER JOIN (SELECT
                products_id, MIN(categories_id) min_categories_id
              FROM
                zen_products_to_categories
              GROUP BY
                products_id) min_ct
  ON pc.products_id=min_ct.products_id
     AND pc.categories_id=min_ct.min_categories_id
WHERE
  ....