Php 检查3条语句的if-else条件

这是我检查id的代码。我想检查sesion id是1还是2或3。如果是1，则相应的查询从db获取数据并执行。但这里我得到的查询是空的

<?php
if($_SESSION['id'] =='1')
{
$sql ="select a.`id` 'User ID', a.`username` 'Username',MAX(b.login_timestamp) 'Last Logged',count(*) 'Total No. of logins for the Month', count(*)/30 'Avg no. of Logins /day'  from users a left join `client_access_log` b  on b.unique_id=a.unique_id  where b.`username` in( 'ghfh','sdd')  and 
`login_timestamp` between DATE_SUB(DATE_FORMAT(NOW(),'%Y-%m-01'), INTERVAL 1 MONTH) and CAST(DATE_FORMAT(NOW(),'%Y-%m-01') AS DATE) GROUP BY a.id order by count(*) desc";
}
elseif($_SESSION['id'] == '2')
{
$sql ="select a.`id` 'User ID', a.`username` 'Username',MAX(b.login_timestamp) 'Last Logged',count(*) 'Total No. of logins for the Month', count(*)/30 'Avg no. of Logins /day'  from users a left join `client_access_log` b  on b.unique_id=a.unique_id  where b.`username` in( 'dff')  and 
`login_timestamp` between DATE_SUB(DATE_FORMAT(NOW(),'%Y-%m-01'), INTERVAL 1 MONTH) and CAST(DATE_FORMAT(NOW(),'%Y-%m-01') AS DATE) GROUP BY a.id order by count(*) desc";
}
elseif($_SESSION['id'] == '3')
{
$sql ="select a.`id` 'User ID', a.`username` 'Username',MAX(b.login_timestamp) 'Last Logged',count(*) 'Total No. of logins for the Month', count(*)/30 'Avg no. of Logins /day'  from users a left join `client_access_log` b  on b.unique_id=a.unique_id  where b.`username` in( 'wededf')  and 
`login_timestamp` between DATE_SUB(DATE_FORMAT(NOW(),'%Y-%m-01'), INTERVAL 1 MONTH) and CAST(DATE_FORMAT(NOW(),'%Y-%m-01') AS DATE) GROUP BY a.id order by count(*) desc";
}
$query = mysql_query($sql) or die(mysql_error());
    if(!$query)
    {
        mysql_close();
        echo json_encode("There was an error running the query: " . mysql_error());
    }
    elseif(mysql_num_rows($query)==0)
    {
        mysql_close();
        echo json_encode("No results returned");
        exit;
    }
    else
    {
        $header = false;
        $output_string = "";
        $output_string .=  "<table border='2'>\n";
        while($row = mysql_fetch_assoc($query))
        {
            if(!$header)
            {
                $output_string .= "<tr>\n";
                foreach($row as $header => $value)
                {
                    $output_string .= "<th>{$header}</th>\n";
                }
                $output_string .= "</tr>\n";
            }
            $output_string .= "<tr>\n";
            foreach($row as $value)
            {
                $output_string .= "<th>{$value}</th>\n";
            }
            $output_string .= "</tr>\n";
        }
        $output_string .= "</table>\n";
    }
    mysql_close();
    echo json_encode($output_string);
        ?>

请尝试从比较中删除“”

<?php
session_start();
if ($_SESSION['id'] == 1)
{
$sql ="select a.`id` 'User ID', a.`username` 'Username',MAX(b.login_timestamp) 'Last Logged',count(*) 'Total No. of logins for the Month', count(*)/30 'Avg no. of Logins /day'  from users a left join `client_access_log` b  on b.unique_id=a.unique_id  where b.`username` in( 'ghfh','sdd')  and 
`login_timestamp` between DATE_SUB(DATE_FORMAT(NOW(),'%Y-%m-01'), INTERVAL 1 MONTH) and CAST(DATE_FORMAT(NOW(),'%Y-%m-01') AS DATE) GROUP BY a.id order by count(*) desc";
}
elseif ($_SESSION['id'] == 2)
{
$sql ="select a.`id` 'User ID', a.`username` 'Username',MAX(b.login_timestamp) 'Last Logged',count(*) 'Total No. of logins for the Month', count(*)/30 'Avg no. of Logins /day'  from users a left join `client_access_log` b  on b.unique_id=a.unique_id  where b.`username` in( 'dff')  and 
`login_timestamp` between DATE_SUB(DATE_FORMAT(NOW(),'%Y-%m-01'), INTERVAL 1 MONTH) and CAST(DATE_FORMAT(NOW(),'%Y-%m-01') AS DATE) GROUP BY a.id order by count(*) desc";
}
elseif ($_SESSION['id'] == 3)
{
$sql ="select a.`id` 'User ID', a.`username` 'Username',MAX(b.login_timestamp) 'Last Logged',count(*) 'Total No. of logins for the Month', count(*)/30 'Avg no. of Logins /day'  from users a left join `client_access_log` b  on b.unique_id=a.unique_id  where b.`username` in( 'wededf')  and 
`login_timestamp` between DATE_SUB(DATE_FORMAT(NOW(),'%Y-%m-01'), INTERVAL 1 MONTH) and CAST(DATE_FORMAT(NOW(),'%Y-%m-01') AS DATE) GROUP BY a.id order by count(*) desc";
}

---

您是否首先启动了会话..by
会话_start（）尝试添加一些调试信息以验证所有变量是否正确。因此，从ifs之前的
echo$\u SESSION['id']
和ifs之后的
echo$sql
开始。这可能会告诉你出了什么问题。另外，停止使用
mysql
，它已经被弃用了。使用
mysqli
或
PDO
。