比较同一张表中的另一行

Question

I have a table with the following structure:

id_language  id_product  description
1            10           AAAA
2            10           BBBB
3            10           AABB
1            11           CCCC
2            11           CCCC
3            11           CCAA

What I want to do is to find all products that have same description in both languages and replace the description of language 2 with an empty value. So in the example above row 1 and 2 would be left untouched. However description of product 11 and language 2 would be set to "". Like this:

id_language  id_product  description
1            10           AAAA
2            10           BBBB
3            10           AABB
1            11           CCCC
2            11           
3            11           CCAA

Is it possible to do this with just SQL query? I am using MySQL.

Answer 1

Assuming you have only two languages per product, this seems to do what you want:

update t join
       (select id_product, max(id_language) as maxidl
        from t
        group by id_product
        having min(description) = max(description)
       ) tt
       on t.id_product = tt.id_product and t.id_language = tt.maxidl
    set description = null;

Answer 2

Use this one For MySql

UPDATE Table SET description=''
WHERE (id_product,id_language) in(
SELECT id_product,MAX(id_language) FROM Table
GROUP BY description,id_product 
HAVING COUNT(id_language)>1
)

Answer 3

This one works (see it working live here in a sqlfiddle):

UPDATE t
JOIN (

    SELECT
    t1.id_product,
    MIN(t1.id_language) AS min_lang,
    t1.description
    FROM t t1
    JOIN t t2 ON t1.id_product = t2.id_product
    AND t1.description = t2.description
    AND t1.id_language != t2.id_language
    GROUP BY t1.id_product

) sq ON t.id_product = sq.id_product
AND t.description = sq.description
SET t.description = ''
WHERE t.id_language > sq.min_lang;