MySql查詢結果中包含多個計數

Question

我有一張桌子

create table posts (
   text varchar(20),
   created_at datetime,
   user_id integer
);

create table users (
   id integer,
   name varchar(20),
   important bolean
);

create table categories (
   id integer,
   name varchar(20),
);
create table categories_posts (
   category_id integer,
    post_id integer
);

想要計算特定時間之間每個類別的帖子數量，結果如下

START_TIME_PERIOD, category, count_all, count_important, count_normal
'2013-03-06 23:40', 'dogs',    20,       5,               15
'2013-03-06 23:40', 'cats',    22,       6,               16
'2013-03-06 23:40', 'birds',   24,       7,               17

其重要性取決於用戶的重要性。

獲得一個例如重要的計數

select '2013-03-06 23:40', categories.name, count(*)
from posts, users, categories
where posts.id = categories_posts.post_id
and categories.id = categories_posts.category_id
and posts.user_id = users.id
and users.important = true
and posts.created_at BETWEEN '2013-03-06 23:40' AND  '2013-03-06 23:20'
group by 1, 2

在單個結果集中獲取三個計數的最佳方法是什么？

謝謝

Answer 1

SELECT ..... , count(*), SUM(IF(user.important,1,0)) as count_important, COUNT(*) - SUM(IF(user.important,1,0)) as count_normal

Answer 2

您可以使用SUM與CASE結合使用，而不是使用COUNT

SELECT COUNT(*) AS count_all, 
    SUM(CASE WHEN important = 1 THEN 1 ELSE 0 END) AS count_important