如何查询 MySQL 以计算数据库字段中的 NULL 值？答案

【问题标题】：How to query MySQL to count NULL values in database field?如何查询 MySQL 以计算数据库字段中的 NULL 值？
【发布时间】：2018-05-04 09:36:28
【问题描述】：

如何查询 MySQL 以计算数据库表列中的“NULL”值。我的查询响应总是 0 打印。

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

print_r($rawm_jan_full);

【问题讨论】：

成功了，我已将 COUNT(trainings_id) 替换为 COUNT(*)

标签： php mysql singlestore

【解决方案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

【讨论】：

【解决方案2】：

请使用 Queryall 而不是 queryRow。

【讨论】：

【解决方案3】：

你可以使用 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);

【讨论】：