Question

I have a table “posts” in MYSQL for some QA forum (for eg. stackoverflow), with the following sample data.

    INSERT INTO POSTS (postID, type, parentID, QuesTitle) VALUES(1,'Q',NULL,'sometext');
    INSERT INTO POSTS (postID, type, parentID, QuesTitle) VALUES(2,'Q',NULL,'randomtext');
    INSERT INTO POSTS (postID, type, parentID, QuesTitle) VALUES(3,'A',1,NULL);
    INSERT INTO POSTS (postID, type, parentID, QuesTitle) VALUES(4,'A',1,NULL);
    INSERT INTO POSTS (postID, type, parentID, QuesTitle) VALUES(5,'Q',NULL,'titletext');
    INSERT INTO POSTS (postID, type, parentID, QuesTitle) VALUES(6,'A',1,NULL);
    INSERT INTO POSTS (postID, type, parentID, QuesTitle) VALUES(7,'A',2,NULL);
    INSERT INTO POSTS (postID, type, parentID, QuesTitle) VALUES(8,'A',2,NULL);

postID is primary key and parentID refers to postID. A “Q” (question) type post can have multiple “A” (answers) posts(shown by their parentID). Only “Q” posts have titles but “A” posts have no titles(NULL)

I want to select the “A” type posts along with their post ID, their parent ID and the Questitle it refers to. For example- required result is-

    postID    parentID    QuesTitle
    3         1           sometext
    4         1           sometext
    6         1           sometext
    7         2           randomtext
    8         2           randomtext

It would be easier using ‘with’ clause CTE but MYSQL doesn’t support it. Can someone help me in achieving it in MYSQL?

Answer 1

Why would you need a CTE?

You can simply do a self-join to get the parentID‘s information:

SELECT a.postID, a.parentID, b.QuesTitle
FROM   posts a
JOIN   posts b ON a.parentID = b.postID
WHERE  a.type = 'A'