内部联接中多个列的多个AND

Question

I have a table of products, a table of custom definitions, and a table of values:

products

id   product_name         price
48   product one          32.99
87   another product      2.50
...etc

fielddefs

id   name
6    brand
9    colour
23   flavour
...etc

fieldvals

product_id   fielddef_id   value
48           6             Rowntree
48           9             Red
48           23            Strawberry
87           6             Cadburys
87           9             Yellow
87           23            Lemon
etc...

I am now trying to do a search using a filter with drop-down selections for each fielddef:

$sql = "SELECT * FROM products INNER JOIN fieldvals ON fieldvals.product_id=products.id WHERE product_name LIKE '%".$q."%' AND (fielddef_id='7' AND value='".$c."') AND (fielddef_id='8' AND value='".$b."') AND (fielddef_id='9' AND value='".$f."') AND (fielddef_id='10' AND value='".$t."') AND (fielddef_id='5' AND value='".$h."') AND (fielddef_id='6' AND value='".$v."')";

An echo of the SQL gives me something like:

SELECT * FROM products INNER JOIN fieldvals ON fieldvals.product_id=products.id WHERE product_name LIKE '%cola%' AND (fielddef_id='7' AND value='Purple') AND (fielddef_id='9' AND value='Apple') AND (fielddef_id='10' AND value='Party') AND (fielddef_id='5' AND value='true') AND (fielddef_id='6' AND value='true')

This code only works for one criteria after the $q - ie you can include $q and $c, or $q and $h, or $q and $v, and it successfully finds matching products, but multiple nested AND statements do not seem to work.

Where am I going wrong?

Answer 1

This link offers a similar question where someone wanted to query from the same "field data" table and wanting multiple conditions.

The issue you are encountering is that for any single record, none of them can have MULTIPLE values for a given column, only a result of comparing multiple records and applying a HAVING COUNT(*) = criteria you are looking for. The other (per my link above) shows that. Now how can this similar approach be applied to your problem.

SELECT 
      P.ID,
      P.Product_Name,
      P.Price
   FROM 
      products P
         INNER JOIN fieldvals FV1
            ON P.id = FV1.product_id 
            AND FV1.FieldDef_ID = '7'
            AND FV1.Value = 'value expected for 7'

         INNER JOIN fieldvals FV2
            ON P.id = FV2.product_id 
            AND FV2.FieldDef_ID = '8'
            AND FV2.Value = 'value expected for 8'

         INNER JOIN fieldvals FV3
            ON P.id = FV3.product_id 
            AND FV3.FieldDef_ID = '9'
            AND FV3.Value = 'value expected for 9'

         (continue same "join" sample above for as many
          criteria conditions you need to add... just keep
          incrementing the alias ... FV1, FV2, FV3, etc...)
   WHERE 
      P.Product_Name like '%your criteria%'