PHP SQL 数据库查询错误信息

Question

这段SQL代码有什么问题吗？我从教程中得到它，但它返回以下错误消息

Database query failed: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'LIMIT 1' at line 1

function get_subject_by_id($subject_id) {
    global $connection;
    $query = "SELECT * ";
    $query .= "FROM subjects ";
    $query .= "WHERE id=" . $subject_id ." ";
    $query .= "LIMIT 1";
    $result_set = mysql_query($query, $connection);
    confirm_query($result_set);
    // if no rows are returned, fetch array will return false
    if ($subject = mysql_fetch_array($result_set)){
    return $subject;
    } else {
    return NULL;

    }
    }

Answer 1

最好回显查询并查看它的样子。

可能 $subject_id 不包含值或包含无效值。如果 $subject_id 是一个字符串，您应该将其转义(使用 mysql_real_escape_string)并在查询中将其放在引号内。

[编辑]

您知道您也可以在字符串中输入 enter，对吗？

// More readable
$query = "
  SELECT *
  FROM subjects
  WHERE id = $subject_id
  LIMIT 1";