MySQL计数范围条件

Question

我有这样的查询

select newscategory.CategoryName, count(distinct newsmain.id)
from newsmain join newscategory on 
newscategory.CategoryName = newsmain.Category 
group by CategoryName

并返回正确的结果，如下所示：

CategoryName  count(distinct newsmain.id)
Acupunctura   1
Neurologie    1
Test Category 2

＆＃34; newsmain＆＃34;表有一个＆＃34; AppPublished＆＃34; datetime字段和我尝试做的是为计数添加一个条件，根据是否＆＃34; AppPublished＆＃34;在两个日期时间变量的范围内。举个例子，我需要这样的结果：

CategoryName  count(distinct newsmain.id)
Acupunctura   0
Neurologie    0
Test Category 1

我是否需要创建子查询，或者是否有办法为此查询添加一些条件？

因为此查询中的任何添加条件导致对＆＃34; CategoryName＆＃34;进行不必要的过滤。列。

Answer 1

您可以使用CASE条件，例如

select newscategory.CategoryName, 
count(CASE WHEN AppPublished BETWEEN date1 and date2 THEN distinct newsmain.id END)
from newsmain join newscategory on 
newscategory.CategoryName = newsmain.Category 
group by CategoryName

（OR）喜欢这个

select newscategory.CategoryName, 
sum(CASE WHEN AppPublished BETWEEN date1 and date2 THEN 1 ELSE 0 END)
from newsmain join newscategory on 
newscategory.CategoryName = newsmain.Category 
group by CategoryName