MySQL DELETE与JOIN条件

Question

I have 3 tables; products, variants, and stock {simplified}

PRODUCTS id name discontinued (ENUM: 0 or 1) etc

VARIANTS id product_id colour size

STOCK id variant_id branch_id

When the user selects to discontinue the PRODUCT I set the discontinued flag to 1. That's fine, but I want to delete the PRODUCT and VARIANTS records altogether if there is no STOCK record of the product. Obviously I can do this using a SELECT query first in PHP but I would like to do it in one mySQL query. This is what I have so far, but it is returning an error from mySQL:

$query = "DELETE FROM prod_lines, 
  JOIN variants ON variants.lineid = prod_lines.id
  WHERE prod_lines.id = '$lineid' AND
  (SELECT COUNT(id) FROM stock WHERE stock.variantid = variants.id) = 0";

Can anybody out there help me come up with the right solution? Maybe there is a better way that doesn't even involve a subquery?

Thanks in advance

Answer 1

I assume that the product_line table in your query is the PRODUCTS table you describe in the beginning of your post.

DELETE prod_lines.*  -- you must specify which table you are deleting from, because there are several tables in the FROM clause
FROM prod_lines
JOIN variants ON variants.lineid = prod_lines.id
LEFT JOIN stock ON stock.variantid = variants.id
WHERE prod_lines.id = @lineid -- your "$lineid" variable here
AND stock.id IS NULL; -- selects only items with no match in the "stock" table

http://sqlfiddle.com/#!2/40a21

Answer 2

Try something like this,the downside is though you have to have two php variables here and also an nested query that you may not be ok with

   DELETE FROM (select COUNT(id) countstock FROM stock s,variants v WHERE s.variantid = v.id and v.productid='$lineid') prod 
    where prod.countstock>1 and prod.productid='$lineid'