合并所有或单个语句的预备语句

Question

Which should i use? In second one there is unknown quantity of statements. I know very little about prepared statements. Trying to change my code from simple queries. And i am stuck here, since it seems to me if i use top one, i'll have to make many request and it will be slower.

$stmt  = $con->prepare("SELECT * FROM dbtable WHERE col1=? AND col2=?");

or

$stmt  = $con->prepare("
    SELECT * FROM dbtable WHERE col1=? AND col2=? UNION ALL
    SELECT * FROM dbtable WHERE col1=? AND col2=? UNION ALL
    SELECT * FROM dbtable WHERE col1=? AND col2=? UNION ALL
    SELECT * FROM dbtable WHERE col1=? AND col2=? UNION ALL
    SELECT * FROM dbtable WHERE col1=? AND col2=? UNION ALL
    SELECT * FROM dbtable WHERE col1=? AND col2=? UNION ALL
    SELECT * FROM dbtable WHERE col1=? AND col2=?
");

edit:

My actual code is:

foreach ($games as $ob)
{
    $sql.= "SELECT * FROM (SELECT gamesdata.rating, gamesdata.name, games.game, games.game_id FROM gamesdata 
        INNER JOIN login ON gamesdata.user_id=login.user_id 
        INNER JOIN games ON games.game_id=gamesdata.game_id 
        WHERE username='".$user."' AND game='".$ob->game."' AND gamespl>0 ORDER BY rating DESC LIMIT 5) DUMMY_ALIAS".$i." UNION ALL ";
    $i++;
}

Trying to change this to prepared statements.

Answer 1

You want to set up your prepared statement once and run it with each of the changed inputs.

$stmt = $con->prepare("SELECT * FROM dbtable WHERE col1=:user AND col2=:game UNION ALL");

$prepared = array('user' => $user); // user doesn't change
foreach ($games as $ob) { // for each game
   $prepared['game'] = $ob->game; // set this queries game
   $stmt->execute($prepared); // execute with current game
   while ($row = $stmt->fetch()) { // iterate over rows
       var_export($row);
   }
}