[英]Compare value in previous row SQL
假設您在sqllite
有一些像這樣的表
c.execute('''CREATE TABLE customers
(customer_id INT, name VARCHAR)''')
c.execute('''CREATE TABLE orders
(order_id INT, quantity INT, order_date DATETIME, customer_id INT)''')
您如何比較兩個不同日期之間的客戶訂單數量?
我已經查詢到了我每天都有客戶計數的地方
SELECT A.customer_id, name, SUM(quantity), strftime('%Y-%m-%d', order_date) d FROM orders " \
"A LEFT JOIN customers B on A.customer_id = B.customer_id "\
"GROUP BY d, A.customer_id " \
"ORDER BY B.name LIMIT 20;
這樣給我一些結果
(0, 'customer_0', 423, '2018-03-27')
(0, 'customer_0', 1054, '2018-03-28')
(1, 'customer_1', 757, '2018-03-21')
(1, 'customer_1', 314, '2018-03-22')
我需要能夠將一行與上一行進行比較,並得到這樣的差異-
customer_0, 631
customer_1, -443
SELECT
C.customer_id,
C.name,
SUM(CASE WHEN strftime('%Y-%m-%d', O.order_date) = S.final_order_date THEN O.quantity END)
-
SUM(CASE WHEN strftime('%Y-%m-%d', O.order_date) = S.first_order_date THEN O.quantity END)
AS delta_value
FROM
customers C
INNER JOIN
(
SELECT
customer_id,
strftime('%Y-%m-%d', MIN(order_date)) first_order_date,
strftime('%Y-%m-%d', MAX(order_date)) final_order_date
FROM
orders
GROUP BY
customer_id
)
S
ON S.customer_id = C.customer_id
INNER JOIN
orders O
ON O.customer_id = C.customer_id
GROUP BY
C.customer_id,
C.name
ORDER BY
C.name
LIMIT
20
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