修复错误：mysql_num_rows（）：提供的参数不是有效的MySQL结果资源

Question

I'm not sure why this is not working:

if($strFilterByStatus != 'all' &&  $strFilterByYear == 'all' && $strFilterByMonth !='all')
{
    $strSQL = "SELECT * FROM tblcase where recovered = '".$strFilterByStatus."' and monthreported = '".$strFilterByMonth."'" ;
}
else if($strFilterByStatus != 'all' &&  $strFilterByYear != 'all' && $strFilterByMonth !='all')
{
    $strSQL = "SELECT * FROM tblcase where recovered = '".$strFilterByStatus."' and yearreported = '".$strFilterByYear."' and monthreported = '".$strFilterByMonth."'" ;
}


if (mysql_num_rows($strSQL)==0)
{
    $strCaseExist = false;
}
else
{
    $SQL=mysql_query($strSQL);  
    $strCaseExist = true;
}

I have 2 different SQL statements and I just want to know if it will return a record or not.

Answer 1

You are not executing the query.check this manual for more details on mysql_num_rows() ,change your code like this

$resrce =mysql_query($strSQL)
if (mysql_num_rows($resrce)==0)

Beware about mysql functions, they are insecure and deprecated. Choose mysqli or pdo

Answer 2

mysql_num_rows requires a resultset to be passed not a string variable. Change to the following code:

$result = mysql_query( $strSQL );
$strCaseExist = (mysql_num_rows($result) == 0) ? false : true;

Answer 3

您必须在检查num行之前执行查询。