Question

For example this query:

SELECT `variants`.* 
  FROM `variants` INNER JOIN `variant_attributes` 
    ON variant_attributes.variant_id = variants.id 
 WHERE (variant_attributes.id IN ('2','5'))

And variant has_many variant_attributes

What I actually want to do is to find which variant has BOTH variant attributes with ID = 2 and 5. Is this possible with MySQL? Bonus Question, is there a quick way to do this with Ruby on Rails, perhaps with SearchLogic?

solution

Thank you Quassnoi for the query you provided, that worked perfectly.

To use on Rails, I used the named_scope below, I think this is simpler to understand for beginners.

Basically named_scope would return {:from => x, :conditions => y} and the lines above were used to setup the y variable.

  named_scope :with_variant_attribute_values, lambda { |values|
    conditions = ["(
            SELECT  COUNT(*)
            FROM    `variant_attributes`
            WHERE   variant_attributes.variant_id = variants.id
                    AND variant_attributes.value IN (#{values.collect { |value| "?" }.join ", "})
            ) = ?
    "]
    conditions = conditions + values + [values.length]
    {
    :from => 'variants', 
    :conditions => conditions
  }}

Answer 1

Assiuming that variant_attributes (variant_id, id) is unique:

SELECT  `variants`.*
FROM    `variants`
WHERE   (
        SELECT  COUNT(*)
        FROM    `variant_attributes`
        WHERE   variant_attributes.variant_id = variants.id
                AND variant_attributes.id IN ('2','5')
        ) = 2