SQL查詢：用戶每月增長的百分比

Question

我有這個簡單的查詢計算每月用戶註冊的數量。

SELECT TO_CHAR(created_at, 'YYYY-MM') AS month, COUNT(user_id) 
FROM users 
GROUP BY month 
ORDER BY month DESC 

我想要的是每個月的增長百分比與前一個月相比。

Answer 1

SQL Fiddle

select 
    month, total, 
    (total::float/lag(total) over (order by month) - 1) * 100 growth 
from (
    select to_char(created_at, 'yyyy-mm') as month, count(user_id) total 
    from users 
    group by month 
) s 
order by month; 
    month | total |  growth  
---------+-------+------------------ 
2013-01 |  2 |     
2013-02 |  3 |    50 
2013-03 |  5 | 66.6666666666667 

Answer 2

SQL Fiddle

的PostgreSQL 9.1.9架構設置：

create table users (created_at date, user_id int); 
insert into users select '20130101', 1; 
insert into users select '20130102', 2; 
insert into users select '20130203', 3; 
insert into users select '20130204', 4; 
insert into users select '20130201', 5; 
insert into users select '20130302', 6; 
insert into users select '20130303', 7; 
insert into users select '20130302', 8; 
insert into users select '20130303', 9; 
insert into users select '20130303', 10; 

查詢1：

select 
    month, 
    UserCount, 
    100 - lag(UserCount) over (order by month asc) 
     * 100.0/UserCount Growth_Percentage 
from 
(
    SELECT TO_CHAR(created_at, 'YYYY-MM') AS month, 
     COUNT(user_id) UserCount 
    FROM users 
    GROUP BY month 
    ORDER BY month DESC 
) sq 

Results：

| MONTH | USERCOUNT | GROWTH_PERCENTAGE | 
------------------------------------------- 
| 2013-01 |   2 |   (null) | 
| 2013-02 |   3 | 33.333333333333 | 
| 2013-03 |   5 |    40 | 

---

Clodo阿爾是正確的，增長比例應使用（Fiddle2）

100.0 * UserCount 
     /lag(UserCount) over (order by month asc) 
     - 100 
     AS Growth_Percentage