dsf1222 2012-02-24 09:53
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MySQL强制查询返回NULL

I have the following:

SELECT q25, COUNT( q25 ) AS count, AVG (q1) AS q1
FROM tresults WHERE id = 'Yes' AND date = 'MARCH2010' AND q25 = '1' 
GROUP BY q25

At the moment, the query returns MySQL returned an empty result set (i.e. zero rows). which is correct - is it possible to get it to return NULL instead?

OR

Is there a way of dealing with this after the event in PHP, such as:

$resultprev = mysql_query($queryprev);
if($resultprev == ''){
// do something
}
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2条回答 默认 最新

  • dongyuan8312 2012-02-24 09:57
    关注

    use mysql_num_rows :

    $resultprev = mysql_query($queryprev);
    $num_rows = mysql_num_rows($resultprev);
    if($num_rows == 0){
       // 0 results !
    }
    

    or you could union a null row :

    SELECT q25, COUNT( q25 ) AS count, AVG (q1) AS q1
    FROM tresults WHERE id = 'Yes' AND date = 'MARCH2010' AND q25 = '1' 
    GROUP BY q25
    
    UNION
    
    SELECT null, null as count, null as q1
    
    本回答被题主选为最佳回答 , 对您是否有帮助呢?
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