大型查询JOINS中的SQL子查询链

Question

I am trying to structure a SQL query with complex nested select operation!

My original SQL query successfully JOINS around 30 tables, the data are retrieved as wanted! However every fetched record in the 30 tables has many records in another table called (Comments)! What I want to do is to atribute every record in the (Comments table) to its record in the other 30 tables by IDs and retrieve them all together in one query. Yet this is not the only challenge, some of the 30 tables have in addition to the records in (Comments table) more records in another table called (extras), so i am looking for additional subquery within the main subquery within a LEFT JOIN inside the outter main query.

To make the idea more clear; without subquery the script will be as following:

$query = $mysqli->query("
SELECT 
parent1.parent1_id,
parent1.child1_id,
parent1.child2_id,
parent1.child3_id,
parent2.parent2_id,
parent2.child1_id,
parent2.child2_id,
parent2.child3_id,
child1.child1_id, 
child1.child1_content,
child2.child2_id, 
child2.child2_content,  
child3.child3_id, 
child3.child3_content
    FROM 
        parent1
    LEFT JOIN child1
        ON child1.child1_id = parent1.child1_id

    LEFT JOIN child2
        ON child2.child2_id = parent1.child2_id

    LEFT JOIN child3
        ON child3.child3_id = parent1.child3_id

    LEFT JOIN followers
        ON parent1.user_id = followers.followed_id
        AND parent1.parent1_timestamp > followers.followed_timestamp
        AND parent1.parent1_id NOT IN (SELECT removed.isub_rmv FROM removed)
        AND parent1.parent1_hide = false
    WHERE 
        followers.follower_id = {$_SESSION['info']}
        {$portname_clause}
    ORDER BY 
        parent1.parent1_timestamp DESC
    LIMIT 
        {$postnumbers} 
    OFFSET 
        {$offset}
")

// Now fetching and looping through the retrieved data

while($row = $query->fetch_assoc()){

    echo $row['child1_content'];
    $subquery1 = $mysqli->query("SELECT extras.child1_id, 
    extras.extrasContent FROM extras WHERE extras.child1_id = 
   {$row['child1_id']}");
    while($row1 = $subquery1->fetch_assoc()){
        echo $row1['extrasContent'];
    }
    echo $row['child2_content'];
    $subquery2 = $mysqli->query("SELECT extras.child2_id, 
    extras.extrasContent FROM extras WHERE extras.child2_id = 
    {$row['child2_id']}");
    while($row2 = $subquery2->fetch_assoc()){
        echo $row2['extrasContent'];
     }

    echo $row['child3_content'];
    $subquery3 = $mysqli->query("SELECT extras.child3_id, 
    extras.extrasContent FROM extras WHERE extras.child3_id = 
    {$row['child3_id']}");
    while($row3 = $subquery3->fetch_assoc()){
        echo $row3['extrasContent'];

        // Here i need to run additional query inside the subquery 3 to retrieve the (Comments table) data beside (extras table)

        $subquery4 = $mysqli->query("SELECT comments.comment_id, comments.comment FROM comments WHERE comments.child3_id = {$row['child3_id']} OR comments.child3_id = {$row3['child3_id']}");
        while($row4 = $subquery4->fetch_assoc()){
        echo $row4['comment'];
        }

    }

} // No sane person would make such code

Because the code above would be totally rediclious i searched for a better way to carry it out, and thats where i came across the subquery concept, but i do not know anything about subqueries, and shortly after i studied it i came up with this messy code, check it below!

I am not posting the origianl code here because it is too long, i am including a virtual example of the tables i want to apply the query on in order to demonstrate the process.

SELECT 
parent1.parent1_id,
parent1.child1_id,
parent1.child2_id,
parent1.child3_id,
parent2.parent2_id,
parent2.child1_id,
parent2.child2_id,
parent2.child3_id
FROM 
    parent1
    LEFT JOIN 
        ( SELECT 
        child1.child1_id, 
        child1.child1_content
    FROM 
        child1 
    WHERE 
        child1.child1_id = parent1.child1_id ) child1
        ( SELECT extras.extrasID, extras.extrasContent
    FROM 
        extras
    WHERE 
        extras.child1_id = child1.child1_id )
        ON parent1.child1_id = child1.child1_id
    LEFT JOIN child2
        ( SELECT 
        child2.child2_id, 
        child2.child2_content
        FROM 
           child2 
        WHERE
            child2.child2_id = parent1.child2_id )
            ( SELECT 
            extras.extrasID, 
            extras.extrasContent
            FROM 
                extras
            WHERE 
                extras.child2_id = child2.child2_id )
                    ON parent1.child2_id = child2.child2_id
                LEFT JOIN child3
                    ( SELECT 
                    child3.child3_id, 
                    child3.child3_content
                FROM 
                    child3
                WHERE 
                    child3.child3_id = parent1.child3_id )
                    ( SELECT 
                        extras.extrasID, 
                        extras.extrasContent 
                    FROM 
                        ( SELECT 
                            comments.comment_id, 
                            comments.comment
                        FROM 
                            comments 
                        WHERE 
                            comments.child3_id = extras.child3_id ) extras
                        JOIN child3 
                             ON extras.child3_id = child3.child3_id )

          ON parent1.child3_id = child3.child3_id
   LEFT JOIN followers
        ON parent1.user_id = followers.followed_id
        AND parent1.parent1_timestamp > followers.follower_timestamp
        AND parent1.parent1_id NOT IN (SELECT removed.isub_rmv FROM removed)
        AND parent1.parent1_hide = false
   WHERE 
        followers.follower_id = {$_SESSION['info']}
        {$portname_clause}
   ORDER BY 
       parent1.parent1_timestamp DESC
   LIMIT 
       {$postnumbers} 
   OFFSET
       {$offset} // <-- Sorry for the bad code formatting!

I am using MySql 5.6.37

I did not get the hang of the subquery concept yet, frankly i got lost and confused as i was studying it and for another reason too mentioned in the note below.

Note: I apologize in advance that i might not be on instant reply because where i live there is no electrecity or ADSL or phones and my USB modem hardly gets signal, i have only two hours of averege three hours a day of electericity generated by a desil generator. i recharge my laptop and check internet and the remaining one-two hours are for other life stuff. I know the joke is on me as i am developing a web project without electricity or permanent internet. BUT LIFE DOES NOT GIVE EVERYTHING! lol.

Answer 1

This is how i solved the problem!

  SELECT 
        parent1.parent1_id,
        parent1.child1_id,
        child1.child1_id,
        child1.child1_content,
        comments.comment_id, 
        comments.comment, 
        comments.child1_id
  FROM parent1 LEFT JOIN 
(
    SELECT comments.comment_id, comments.comment, comments.child1_id
      FROM 
    (
        SELECT comments.comment_id,comments. comment, comments.child1_id
          FROM comments
    ) comments JOIN child1
        ON comments.child1_id = child1.child1_id
) comments
    ON child1.child1_id = comments.

It needs some aliases and then it's good to go.