Question

Table tags:
article_id     tag
1              Language
1              Java
1              c++
2              Language
2              c++
3              c++

and how can I write SQL(s) query(s) to make the data like below:

Table tags_relations:

tag1        tag2     relations_degree
Language    C++     2
Language    Java    1

note: if the tag refers to the same article then the relations_degree + 1

The purpose of this approach is to calculate the relations between tags, can any one help me on this?

Answer 1

Something like:

SELECT A.tag AS tag1, B.tag AS tag2, COUNT(*) as relations_degree
FROM tags A
     INNER JOIN tags B ON A.article_id = B.article_id
WHERE A.tag = 'Language' AND a.tag <> b.tag
GROUP BY A.tag, B.tag
ORDER BY B.tag ASC

Based on your example, I assumed you were limiting it to tag1 = ‘Language’, otherwise there’s the case of tag1 = Java, tag2 = c++, relations_degree = 1. To get that:

SELECT A.tag AS tag1, B.tag AS tag2, COUNT(*) as relations_degree
FROM tags A
     INNER JOIN tags B ON A.article_id = B.article_id
WHERE A.tag > b.tag
GROUP BY A.tag, B.tag
ORDER BY B.tag ASC