I have indexed the SKU column in both DB tables. How do I speed this query up? (There are 20,000+ records in table "Download")
I was using WHERE NOT IN and thought I could speed it up some by using a LEFT JOIN and IS NULL.
Thanks for your help!!
$query1 = $conn->query('SELECT DISTINCT `Download`.SKU FROM `Download` LEFT JOIN MissingDescriptions ON `Download`.SKU = MissingDescriptions.SKU WHERE MissingDescriptions.SKU IS NULL');