Selecting records from one table

Question

I have following table (tbl_product_rel):

id  product_id  attr_id
1      1           10
2      1           15
3      1           20
4      2           6
5      2           9
6      3           10
7      3           15
8      3           20
9      4           15

I want to get product_ids which have attr_ids exactly equal to 10,15,20. If I use MySQL IN

SELECT DISTINCT(product_id) FROM tbl_product_rel WHERE attr_id IN (10,15,20)

so I get also product_id which has attr_id equal to 15, but it does not have attr_ids 10 and 20.

Any ideas ?

Answer 1

您可以使用这样的查询，但我不知道这是否是最佳解决方案:)

SELECT * FROM tbl_product_rel WHERE attr_id IN (10,15,20) GROUP BY product_id HAVING COUNT(product_id) = 3

Answer 2

The reason why you might get impression that your query does not work is probably due to DISTINCT function.
Think what is your desired output? You want get all product_id where attr_id is 10, 15 or 20. It means you want following ids:

id  product_id  attr_id
1      1 OK          10 
2      1 OK          15
3      1 OK          20
4      2 NO          6
5      2 NO          9
6      3 OK          10
7      3 OK          15
8      3 OK          20
9      4 OK          15

so the basic query without distinct should return:

1, 1, 1, 3, 3, 3, 4

if you use distinct, you will get unique ids:

1, 3, 4 

I believe this is what you get.

Chances are you want "id" instead of "product_id".

UPDATE:

Ahh I might now what is your problem. You expect to get product_id which satisfies all 3 conditions. You cannot use IN because IN joins ids with OR . The query that you have written could be rewritten as:

`SELECT DISTINCT(product_id) FROM tbl_product_rel WHERE attr_id = 10 OR attr_id = 15 OR attr_id = 20`. 

If you are sure that there are no duplicates (ie. 2 records with attr_id = 20), your solution would be

`SELECT product_id FROM tbl_product_rel WHERE attr_id IN (10, 15, 20) GROUP BY product_id HAVING count(*) = 3

but this will not work if you allow duplicates, for example in this scenario:

id  product_id  attr_id
1      1          10 
2      1          20
3      1          20

you will get 1 but you shouldn't (according to what you need). Plase let me know if you allow such scenarios.

Answer 3

It sounds like you want only product_ids with all three attribute ids. You can do it with some ugly subqueries:

SELECT DISTINCT(product_id) FROM tbl_product_rel
  WHERE product_id IN 
    (SELECT product_id FROM tbl_product_rel WHERE attr_id=10)
  AND product_id IN
    (SELECT product_id FROM tbl_product_rel WHERE attr_id=15)
  AND product_id IN
    (SELECT product_id FROM tbl_product_rel WHERE attr_id=20)

You could also do some uglier joins.

Answer 4

删除独特的功能：

SELECT product_id FROM tbl_product_rel WHERE attr_id IN (10,15,20)