MySQL从两个表中进行多重选择（过滤）

Question

I have two tables at my DB that i want to make a select query First one keeps the product id (int) and if the product is published The second table keeps the filters, and matches with id_product (which is basicaly the product_id from Products) . at id_filter_child we have the value

products

product_id,
published

filters

id_pro_fil,
id_product,
id_filter_child

My tables now are:

products

1     yes
2     yes
3     no

filters

10   1    4
11   1    5
12   2    4
13   2    6
14   2    7

So that is my DB at the moment. From input i have the filters that i want to search So i want to select all products with filter=4 i use:

SELECT * FROM products,filters
WHERE products.product_id=filters.id_product
     AND products.published='1'
     AND filters.id_filter_child='4'

That one works!

Now i need to select all products with filter 4 AND 6. I use:

SELECT * FROM products,filters
WHERE products.product_id=filters.id_product
     AND products.published='1'
     AND filters.id_filter_child='4'
     AND filters.id_filter_child='6'

but i doesnt work (as a result i would want the product with id=2)

Some help please

Thanks in advance

Answer 1

Try this:

SELECT p.*
FROM products p
LEFT JOIN filters ON p.product_id = f.id_product
WHERE p.published='1' AND f.id_pro_fil IN (4,6)

Answer 2

Consider your logic:

 AND filters.id_filter_child='4'
 AND filters.id_filter_child='6'

You're requiring every filter_child in the database to have two DIFFERENT values at the same time. "this record must be a banana and a ferrari simutaneously"

You want an OR instead:

AND ((filter_child = '4') OR (filter_child = '6'))

(note the extra brackets), or more compactly:

AND (filter_child IN ('4', '6'))

--- comment followup

If you need both values to be attached to a record,t hen you'll have to use some extra logic:

SELECT *, COUNT(filters.id_filter_child IN ('4', '6')) AS count
FROM products,filters
WHERE products.product_id=filters.id_product
     AND products.published='1'
     AND filters.id_filter_child IN ('4', '6')
GROUP BY filters.id_filter_child
HAVING count = 2

The where returns only the records that have either 4 or 6 for filter_child - this will catch records that have at least ONE of those two values. The COUNT(..) + GROUP + HAVING business will then filter out all but those records that have BOTH of the values.

Answer 3

You can use OR or IN

SELECT * FROM products,filters 
  WHERE products.product_id=filters.id_product 
      AND  products.published='1' 
      AND (filters.id_filter_child='4' OR filters.id_filter_child='6')

SELECT * FROM products,filters 
  WHERE products.product_id=filters.id_product 
      AND  products.published='1' 
      AND filters.id_filter_child IN (4,6)

Answer 4

you should OR in between the two conditions:

SELECT * FROM products,filters
WHERE products.product_id=filters.id_product
     AND products.published='1'
     AND filters.id_filter_child='4'
     OR filters.id_filter_child='6'

but to make your sql smaller and simpler you can use IN operator also:

SELECT * FROM products,filters
WHERE products.product_id=filters.id_product
     AND products.published='1'
     AND filters.id_filter_child IN(4,6)

Answer 5

If you want to select all products, then there is no reason to also include the filters. One approach is to use an aggregation and having clause:

SELECT p.*
FROM products p JOIN
     filters f
     ON p.product_id = f.id_product
WHERE p.published = '1'
GROUP BY p.product_id
HAVING SUM(f.id_filter_child = '4') > 0 AND
       SUM(r.id_filter_child = '6') > 0

This returns product that have both filter 4 and filter 6.

Note that I also fixed the query to use proper, explicit join syntax.

I like this method for "set-within-sets" subqueries, because it is quite general. You can add another filter to the HAVING clause with a similar condition. You could get everything with 4 but not 6 by changing the second > 0 to = 0 .