如何使用PHP从Mysql数据库中选择随机列值

Question

I'm trying to fetch random column from database using Rand() function. It's returning random value but many time it's returning duplicate. This is what my database table look like.

|------
|Column|Type|Null|Default
|------
|no|int(30)|No|
|postid|varchar(100)|Yes|NULL
|byuser|varchar(32)|Yes|NULL
|likeslimit|int(30)|No|
|createdon|date|No|
|-----

And this is what my PHP code is.

$query = mysqli_query($mysql, "SELECT postid FROM history ORDER BY Rand() Limit 1");
    if (mysqli_num_rows($query) == 1) {
        while ($row = mysqli_fetch_assoc($query)) {
            echo $row['postid'];
        }
    }

I want it to always return random never the same till the end of data reached.

Answer 1

don't use loop and condition you want only 1 limit try this

 $query = mysqli_query($mysql, "SELECT postid FROM history ORDER BY Rand() Limit 1");

        $row = mysqli_fetch_assoc($query)
        echo $row['postid'];

Answer 2

This is the way RAND in mysql works and will repeat the results from time to time. But you can achieve such functionality by using mysql with php.

$query = mysqli_query($mysql, "SELECT postid FROM cacheTable WHERE 1 ORDER BY RAND() LIMIT 1");
$row = mysqli_fetch_assoc($query);
$foundId = (int)$row['postid'];

if((int) $foundId === 0) { // NO records left in cacheTable then fill it up again
    mysqli_query($mysql, "INSERT INTO cacheTable (postid) SELECT postid FROM history");
    $query = mysqli_query($mysql, "SELECT postid FROM cacheTable WHERE 1 ORDER BY RAND() LIMIT 1");
    $row = mysqli_fetch_assoc($query);
    $foundId = (int) $row['postid'];
}

mysqli_query($mysql, "DELETE FROM cacheTable WHERE postid=".$foundId); // DELETE the record

$query = mysqli_query($mysql, "SELECT * FROM history WHERE postid=".$foundId);
$result = mysqli_fetch_assoc($query);

cacheTable will have only one column - ID (primary key) which will hold the corresponding ID (primary key) from history. cacheTable structure:

|------
|Column|Type|Null|Default
|------
|postid|varchar(100)|Yes|NULL
|-----

cacheTable will fill with all the ids from history table (it will be done once the cacheTable is empty). You will select rand result from the cacheTable and you will delete it then so it will not appear in the next selects. When we are out of records in cache table it will populate again.

NB: this approach has one major drawback - when you have new entries in history table they won't be available in cache table until it is empty and filled again.

Answer 3

This is the code Samir Nabil Suggested :

session_start();
$_SESSION['dupes'] = array();
$query = mysqli_query($mysql, "SELECT postid FROM history ORDER BY Rand() Limit 1");
    if (mysqli_num_rows($query) == 1) {
        while ($row = mysqli_fetch_assoc($query)) {
            if (!in_array($row['postid'],$_SESSION['dupes'])){
                 echo $row['postid'];
                 $_SESSION['dupes'][] = $row['postid'];
            }
        }
    }