日期比較

SQL 報表製作

Tyler Pernes

Learning & Development Consultant

要回答的問題

上月 vs 前一個月？
滾動 7 天？

original_table
+------------+----------+
| date       | revenue  |
|------------+----------+
| 2018-01-01 | 400      |
| 2018-01-02 | 380      |
| 2018-01-03 | 625      |
+------------+----------+

月對月比較

LAG(value, offset) 會輸出當前列「之前」第 offset 列的 value。
LEAD(value, offset) 會輸出當前列「之後」第 offset 列的 value。

月對月比較

步驟 1：顯示每月營收

SELECT
    DATE_PART('month',date) AS month,
    SUM(revenue) as current_rev
FROM original_table
GROUP BY month;

步驟 2：前一個月的營收

SELECT
    DATE_PART('month',date) AS month,
    SUM(revenue) as current_rev,
    LAG(SUM(revenue)) OVER (ORDER BY DATE_PART('month',date)) AS prev_rev
FROM original_table
GROUP BY month;

月對月比較

步驟 3：計算百分比變化

SELECT
    DATE_PART('month',date) AS month,
    SUM(revenue) as current_rev,
    LAG(SUM(revenue)) OVER (ORDER BY DATE_PART('month',date)) AS prev_rev,
    SUM(revenue)
    /
    LAG(SUM(revenue)) OVER (ORDER BY DATE_PART('month',date))-1 AS perc_change
FROM original_table
GROUP BY month;

月對月比較

步驟 3：計算百分比變化

+--------+--------------+-----------+--------------+
| month  | current_rev  | prev_rev  | perc_change  |
|--------+--------------+-----------+--------------|
| 01     | 15000        | null      | null         |
| 02     | 14000        | 15000     | -.06         |
| 03     | 21000        | 14000     | .50          |
+--------+--------------+-----------+--------------+

滾動計算

只計入「7 列」

新子句：ROWS BETWEEN

SUM(value) OVER (ORDER BY value ROWS BETWEEN N PRECEDING AND CURRENT ROW)

滾動計算

滾動加總查詢

SELECT 
    date,
    SUM(SUM(revenue)) OVER 
    (ORDER BY date ROWS BETWEEN 6 PRECEDING AND CURRENT ROW) AS weekly_revenue
FROM original_table
GROUP BY date;

新資料表：web_data

web_data
+------------+-------------+--------+
| date       | country_id  | view   |
|------------+-------------+--------|
| 2018-01-01 | 1           | 24313  |
| 2018-01-01 | 2           | 3768   |
| 2018-01-01 | 3           | 26817  |
+------------+-------------+--------+

一起來練習吧！

SQL 報表製作