如何查询MySQL以计算数据库字段中的NULL值？

Question

如何查询MySQL来计算＆＃39; NULL＆＃39;数据库表列中的值。我的回复查询总是0打印。

igraph

Answer 1

$rawm_jan_full=Yii::app()->db->createCommand("SELECT COUNT(case when trainings_id is null then 1 else trainings_id end ) AS trail_list from children WHERE MONTH(timestamp) = '1' AND YEAR(timestamp) ='".$previous_year."' AND trainings_id IS NULL ")->queryRow();

 Replace COUNT(trainings_id )  with    COUNT(case when trainings_id is null then 1 else trainings_id end ) in order to include null in your count result

Answer 2

请使用Queryall而不是queryRow。

Answer 3

您可以使用Queryall

$rawm_jan_full=Yii::app()->db->createCommand("SELECT COUNT(trainings_id) AS trail_list from children WHERE MONTH(timestamp) = '1' AND YEAR(timestamp) ='".$previous_year."' AND trainings_id IS NULL ")->Queryall();

print_r($rawm_jan_full);