将多个表中的多个插入和选择语句合并到一个查询中？

Question

I have these all running as a cron job PHP and it is working, but seems to go slow and I don't think it's very efficient. There are 5 queries and the basic idea behind it is to find new SKU's in the table and insert them into a MasterSKU table.

INSERT INTO MasterSKU (SKU)
SELECT DISTINCT SKU
FROM   AmazonListings
WHERE  NOT EXISTS (SELECT SKU
                   FROM   MasterSKU
                   WHERE  AmazonListings.SKU = MasterSKU.SKU);

INSERT INTO MasterSKU (SKU)
SELECT DISTINCT SKU
FROM   ShopifyListings
WHERE  NOT EXISTS (SELECT SKU
                   FROM   MasterSKU
                   WHERE  ShopifyListings.SKU = MasterSKU.SKU);

INSERT INTO MasterSKU (SKU)
SELECT DISTINCT SKU
FROM   eBayListings_1
WHERE  NOT EXISTS (SELECT SKU
                   FROM   MasterSKU
                   WHERE  eBayListings_1.SKU = MasterSKU.SKU);

INSERT INTO MasterSKU (SKU)
SELECT DISTINCT SKU
FROM   eBayListings_2
WHERE  NOT EXISTS (SELECT SKU
                   FROM   MasterSKU
                   WHERE  eBayListings_2.SKU = MasterSKU.SKU);

INSERT INTO MasterSKU (SKU)
SELECT DISTINCT SKU
FROM   eBayListings_3
WHERE  NOT EXISTS (SELECT SKU
                   FROM   MasterSKU
                   WHERE  eBayListings_3.SKU = MasterSKU.SKU);

I am then going in one by one in the PHP script and using mysqli_query to perform each individual query.

Is it possible to group all of these, even though they are all coming FROM different tables? Or is there a better, more optimized way to do this?

Answer 1

The answer is no and yes.

It is no because if you want to extract data from multiple tables that are not related to each other, you need to use separate queries.

It is yes because in sql you can use union to append the results of multiple queries together - provided they have the same number of fields.

INSERT INTO MasterSKU (SKU)
    (SELECT DISTINCT SKU
     FROM   AmazonListings
     WHERE  NOT EXISTS (SELECT SKU
                   FROM   MasterSKU
                   WHERE  AmazonListings.SKU = MasterSKU.SKU))
     union
     (SELECT DISTINCT SKU
     FROM   ShopifyListings
     WHERE  NOT EXISTS (SELECT SKU
                   FROM   MasterSKU
                   WHERE  ShopifyListings.SKU = MasterSKU.SKU)
     union ...