php - mysql_num_rows 返回 1

Question

为什么下面的代码返回 1，尽管字段 group_members 中没有元素？

$conn = mysql_connect($host,$user,$pass);

@mysql_select_db($db);

$sql = "
    SELECT 
        group_members
    FROM
        tbl_group
    WHERE
        group_id = '6'      
";

$res = mysql_query($sql);

$rows = mysql_num_rows($res);

echo $rows;

?>

Answer 1

您编写的 SQL 将选择所有具有 group_id = 6 的行，然后返回字段 group_members 的值而不考虑内容。要得到你想要的，请尝试:

SELECT group_members FROM tbl_group WHERE group_id = 6 AND group_members <> '' // Depending on type might also be <> NULL or <> 0