本文介绍了MySQL强制查询返回NULL的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
我有以下几点:
SELECT q25, COUNT( q25 ) AS count, AVG (q1) AS q1 FROM tresults WHERE id = 'Yes' AND date = 'MARCH2010' AND q25 = '1' GROUP BY q25目前,查询返回 MySQL 返回一个空结果集(即零行). 这是正确的 - 是否有可能让它返回 NULL 代替?
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?
或
PHP中有没有办法在事件之后处理这个,比如:
Is there a way of dealing with this after the event in PHP, such as:
$resultprev = mysql_query($queryprev); if($resultprev == ''){ // do something } 推荐答案use mysql_num_rows :
$resultprev = mysql_query($queryprev); $num_rows = mysql_num_rows($resultprev); if($num_rows == 0){ // 0 results ! }或者你可以联合一个空行:
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更多推荐
MySQL强制查询返回NULL
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