Question

I’m trying to get a product search to work properly in MySQL 5.0.88.

Basic setup: I have table A with products

A.id
A.ean
A.styleNo
A.price
A.seller (ID e.g. 123, 456)

And a table B with pricelists

B.name
B.ean
B.alt_price
B.seller

Sellers can define optional pricelists, which are matched to the user doing the search. My search more or less looks like this:

    SELECT A.styleNo, A.price, B.price
    FROM arts A
        LEFT JOIN pricelists B ON
                B.seller = A.seller 
            AND B.ean = A.ean 
            AND B.alt_price != 0
    WHERE...
    // pricelists
    AND ( B.name = "some_name" AND B.seller = "123" ) OR ( next applicable seller ) ...

So after the LEFT JOIN, I’m including all items from a pricelist by name and seller.

This works ok as it selects both the regular price (A) and alt_price (B) and I can check for existing alt_price when displaying the results to show the correct price to the user.

However if the seller does not give an alt-price to all of his products, I’m now displaying the product with the price from A, when in fact I DON’T want to display products from this seller which do not have a pricelist entry at all (think regional assortment).

So if user X has a pricelist “abc” and seller 123 has 500 products, 200 of which are on the pricelist “abc”, I only want to display the 200 products and not 500 with 200 in the correct price.

I tried to use B.alt_price != 0 in the LEFT JOIN, but this doesn’t help, because all items on there have a price.

Question
Is there a way to do this in the actual search or do I have to do it in the results loop, which I’m not really keen on doing.

Answer 1

Ok. Finally found the solution.

The problem is, the search will contain multiple sellers, some of whome use pricelists and some who don’t.

• If I do an INNER JOIN on pricelists B, I will not get the products of sellers who don’t use pricelists as they will not be have any entry in B.
• If I do a LEFT JOIN on pricelists B, all entries will have either NULL or pricelist B values, so when I’m searching for a seller who uses pricelists for some of his products, I will always get his full range, regardless of alt_price specified
• If I try to filter these unwanted records (seller uses pricelists, exclude products which are not on it), by adding B.alt_price != 0 to the WHERE clause, I’m also excluding all products from sellers not using pricelists.

I solved it like this:
– I’m having to construct this line anyway:

LEFT JOIN pricelists B ON
       // dynamic construct depending on number of sellers using pricelists matched to user
            B.seller = A.seller 
        AND B.ean = A.ean 
        AND B.alt_price != 0

• So I created another variable, that includes all seller IDs who use pricelists and are applicable to this user. Looks like this:

  123,456,789…

• I add this to the WHERE clause:

  AND ( IF( A.seller IN ( 123,456,789… ), B.alt_price IS NOT NULL,1 ) )

This way, I’m checking
(a) if the record is from a pricelist seller applicable to the user, and
(b) if that’s the case, the records must not have a NULL value in the b.alt_price, which records not being on the pricelist will have, since sql adds NULL to all records not on the pricelist B when LEFT JOINING.

That was difficult…