LIMIT查询

Question

我正在建立一个推荐系统，我只想显示推荐中的前1名，而不是全部。这是代码

$movies = mysqli_query($db, "select * from practice");

while ($movie=mysqli_fetch_array($movies))
{
    $users=mysqli_query($db,"select username from users where id =$movie[user_id]");
    $username=mysqli_fetch_array($users);

    $matrix[$username['username']] [$movie['image']] = $movie ['ratings'];
}


$users=mysqli_query($db,"select username from users where id=$_GET[id]");
$username=mysqli_fetch_array($users);
?>
            <div class="panel panel-default">

                <div class="panel-heading">
                    <h2>
                        <a class="btn btn-info" href="index.php"> Back </a>
                    </h2>
                </div>

                <div class="panel-body">

                    <table class="table table-striped">
                        <th>Clothes</th>
                        <th>Rating</th>
<?php 
    $recommendation=array();

    $recommendation = getRecommendation($matrix,$username['username']);
    foreach($recommendation as $movie => $rating) {
?>
                        <tr>
                            <td>
                                <?php echo "<img src='images/".$movie."' >"; ?>
                            </td>

                            <td>
                                <?php echo $rating  ; ?>
                            </td>
                        </tr>
<?php } ?>
                    </table>
                </div>

Answer 1

您应该在SQL查询中使用LIMIT。

LIMIT查询

如果从结果集中只需要指定数量的行，请在> query中使用LIMIT子句，而不是获取整个结果集并丢弃多余的数据。

MySQL有时会优化具有LIMIT row_count子句而没有HAVING子句的查询

mysql> SELECT * FROM ratings ORDER BY category;
+----+----------+--------+
| id | category | rating |
+----+----------+--------+
|  1 |        1 |    4.5 |
|  5 |        1 |    3.2 |
|  3 |        2 |    3.7 |
|  4 |        2 |    3.5 |
|  6 |        2 |    3.5 |
|  2 |        3 |    5.0 |
|  7 |        3 |    2.7 |
+----+----------+--------+

mysql> SELECT * FROM ratings ORDER BY category LIMIT 1;
+----+----------+--------+
| id | category | rating |
+----+----------+--------+
|  1 |        1 |    4.5 |
+----+----------+--------+

https://dev.mysql.com/doc/refman/8.0/en/select.html

如何仅显示单个数组？

1 个答案:

LIMIT查询