Question

这可能非常简单 - 但我正在撕裂我的头发。数据库正在使用cPanel（MariaDB 10.1.28）

继承人的情景

1表被称为＆＃34;警告＆＃34;
1列名为＆＃34; WARNING_REASON＆＃34; （VARCHAR） warning_reason包含各种＆＃34;原因＆＃34;
1列名为＆＃34; WARNING_LEVEL＆＃34; （VARCHAR）它包含＆＃34; VERBAL＆＃34;，＆＃34; LEVEL 1＆＃34;或＆＃34; LEVEL 2＆＃34;

我需要在5列表格中的php中输出这些数据

警告原因
以warning_reason
匹配＆＃34; VERBAL＆＃34;的行总数按warning_reason分组
匹配＆＃34; LEVEL 1＆＃34;按warning_reason分组
匹配＆＃34; LEVEL 2＆＃34;按warning_reason分组

Answer 1

您可以使用子查询来完成此任务：

SELECT t1.warning_reason
, (SELECT COUNT(*) FROM warnings s1 WHERE s1.warning_reason = t1.warning_reason) AS total_count
, (SELECT COUNT(*) FROM warnings s2 WHERE s2.warning_reason = t1.warning_reason AND s2.warning_level = \'VERBAL\') AS verbal_count
, (SELECT COUNT(*) FROM warnings s3 WHERE s3.warning_reason = t1.warning_reason AND s3.warning_level = \'LEVEL 1\') AS level1_count
, (SELECT COUNT(*) FROM warnings s4 WHERE s4.warning_reason = t1.warning_reason AND s4.warning_level = \'LEVEL 2\') AS level2_count
FROM warnings t1
GROUP BY t1.warning_reason

Answer 2

您可以使用条件聚合：

select warning_reason,
    count(*) as total_warnings,
    sum(warning_level = 'VERBAL')  as verbal_warnings,
    sum(warning_level = 'LEVEL 1') as level1_warnings,
    sum(warning_level = 'LEVEL 2') as level2_warnings
from warnings
group by warning_reason

这比运行多个子选择更短，可能更快。

请注意，在MySQL类似warning_level = 'VERBAL'的布尔表达式中，返回1或0（如果NULL，则返回warning_level is NULL。

如果您需要符合标准的查询，可以将行更改为

sum(case when warning_level = 'VERBAL' then 1 else 0 end) as verbal_warnings,

或

sum(case warning_level when 'VERBAL' then 1 else 0 end) as verbal_warnings,

或

count(case warning_level when 'VERBAL' then 1 else null end) as verbal_warnings,

因为NULL是ELSE的默认值，你也可以跳过它

count(case warning_level when 'VERBAL' then 1 end) as verbal_warnings,

以下内容也适用于MySQL，但我不确定其他系统是否会以相同的方式对其进行评估：

count(warning_level = 'VERBAL' or null) as verbal_warnings,

一页上显示多个COUNT（*）

2 个答案: