CODEWITHSUNDEEP
phpmysqlif-statement
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Reputation: 10218

How to implement a PHP condition using pure SQL?

I have this tables structure:

// Posts
+----+------------+-----------------------+----------------+-------------+
| id |   title    |        content        |  money_amount  |  author_id  |
+----+------------+-----------------------+----------------+-------------+
| 1  | title 1    | content 1             | NULL           | 12345       |
| 2  | title 2    | content 2             | 25             | 42355       |
| 3  | title 3    | content 3             | 5              | 53462       |
| 4  | title 4    | content 4             | NULL           | 36346       |
| 5  | title 5    | content 5             | 15             | 13322       |
+----+------------+-----------------------+----------------+-------------+
//                                          ^^ NULL means this post is free


// Money
+---------+--------------+
| post_id | user_id_paid | 
+---------+--------------+
| 2       | 42355        |  // He is author of post
| 2       | 34632        |  // This row means besides author, this user 34632 can see this post too. Because he paid the money of this post.
| 3       | 53462        |  // He is author of post
| 5       | 13322        |  // He is author of post
| 3       | 73425        |  // This row means besides author, this user 34632 can see this post too. Because he paid the money of this post.
+---------|--------------+

Note1: All post_id(s) in the Money table are belong to those posts which are non-free.

Note2: Always there is a row belong to author of post (which is non-free) in the Money table.

Note3: Money table is just to determines who can see such a post.

Now this user $_SESSION['current_user'] = '23421' wants to see this post id = 2. Here is my code:

$stm = $this->dbh->prepare(SELECT * FROM Posts WHERE id = '2');
$stm->execute();
$result = $stm->fetch(PDO::FETCH_ASSOC);

if ( $result[money] == '') {   // money_amount is NULL in the Posts table
    this post is free and everybody can see it
} else {

    $stm = $this->dbh->prepare(SELECT count(1) FROM Money WHERE post_id = '2' and user_id = $_SESSION['current_user']);
    $num_rows = $stm->fetchColumn();

    if($num_rows){
        $paid = true;  // This means current user paid the cost of post and he can see it.
    } else {
        $paid = false; // this means current user didn't pay the cost of post and he cannot see it.
    }
}

I want to know, can I implement those two query in one query and do that condition using MySQL instead of PHP ?

Upvotes: 1

Views: 59

Answers (2)

RomanPerekhrest
RomanPerekhrest

Reputation: 92854

Here is solution using IF and EXISTS functions(MySql):

...
$stmt = $conn->prepare(" 
        SELECT IF(p.money_amount,1,0) as notfree, 
        EXISTS(SELECT * FROM `Money` WHERE `post_id` = ? AND`user_id_paid` = ?) as paid
        FROM `Posts` p WHERE p.id = ? ");

$stmt->execute([2, $_SESSION['current_user'], 2]);
$result = $stmt->fetch(\PDO::FETCH_ASSOC);

if (!$result['notfree']) {  // post is free
    // this post is free and everybody can see it
} else {
    $paid = ($result['paid'])? true : false; 
}

Upvotes: 1

frz3993
frz3993

Reputation: 1635

You can use a join, and the query below uses LEFT JOIN.

SELECT * FROM Money
LEFT JOIN Posts ON Money.post_id = Posts.id
WHERE ((Posts.money_amount IS NOT NULL AND Money.user_id_paid = :userId)
      OR Posts.money_amount IS NULL) AND Posts.id = :postId

Note that :userId is a placeholder for PDO parameterized query, where you should bind the parameter to the placeholder before execution. Like:

$postId = 2;
$stmt->bindParam('userId', $_SESSION['current_user']);
$stmt->bindParam('postId', $postId);

Also note that when binding the placeholder name doesn't need the colon. Using a RIGHT JOIN means you SELECT from the Posts table and join the Money table.

Upvotes: 1

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