How check value by consecutive date variable - sql

Question

I have database table in SNOWFLAKE, where I need check for each customer if there is FLAG_1 == 1 at minimum 3 days in row. Flag_1 indicates whether the order contained any specific goods. And create new table with customer_id and flag_2. I really don't know how to handle this problem.
Sample table:
CREATE TABLE TMP_TEST
(
CUSTOMER_ID INT,
ORDER_DATE DATE,
FLAG_1 INT
);
INSERT INTO TMP_TEST (CUSTOMER_ID, ORDER_DATE, FLAG_1)
VALUES
(001, '2020-04-01', 0),
(001, '2020-04-02', 1),
(001, '2020-04-03', 1),
(001, '2020-04-04', 1),
(001, '2020-04-05', 1),
(001, '2020-04-06', 0),
(001, '2020-04-07', 0),
(001, '2020-04-08', 0),
(001, '2020-04-09', 1),
(002, '2020-04-10', 1),
(002, '2020-04-11', 0),
(002, '2020-04-12', 0),
(002, '2020-04-13', 1),
(002, '2020-04-14', 1),
(002, '2020-04-15', 0),
(002, '2020-04-16', 1),
(002, '2020-04-17', 1);
Expected output table:
CUSTOMER_ID FLAG_2
001 1
002 0

Answer 1

Maybe this can be help:
with calcflag as (
select customer_id, IFF( sum(flag_1) over (PARTITION by customer_id order by order_date rows between 3 preceding and 1 preceding) = 3, 1, 0 ) as new_flag
from tmp_Test)
select customer_id, max(new_flag) flag_2
from calcflag
group by 1
order by 1;
+-------------+--------+
| CUSTOMER_ID | FLAG_2 |
+-------------+--------+
| 1 | 1 |
| 2 | 0 |
+-------------+--------+

Answer 2

using COUNT_IF also works:
with calcflag as (
select
customer_id,
IFF(
count_if(flag_1 = 1) over (
PARTITION by customer_id
order by order_date
rows between 2 preceding and current row
) = 3, 1, 0
) as new_flag
from tmp_Test
)
select
customer_id,
max(new_flag) flag_2
from calcflag
group by 1
+-------------+--------+
| CUSTOMER_ID | FLAG_2 |
|-------------+--------|
| 1 | 1 |
| 2 | 0 |
+-------------+--------+

Answer 3

Snowflake supports MATCH_RECOGNIZE which is the easiest way to detect advanced patterns across multiple rows:
To find 3 or more occurences the pattern is PATTERN ( a{3,}):
SELECT *
FROM TMP_TEST
MATCH_RECOGNIZE (
PARTITION BY CUSTOMER_ID
ORDER BY ORDER_DATE
MEASURES MATCH_NUMBER() AS mn
ALL ROWS PER MATCH WITH UNMATCHED ROWS
PATTERN ( a{3,} )
DEFINE a AS FLAG_1 = 1
) mr
ORDER BY CUSTOMER_ID, ORDER_DATE;
Output:
Collapsing to single row per group:
SELECT CUSTOMER_ID, COALESCE(MIN(MN),0) AS FLAG_2
FROM TMP_TEST
MATCH_RECOGNIZE (
PARTITION BY CUSTOMER_ID
ORDER BY ORDER_DATE
MEASURES MATCH_NUMBER() AS mn
ALL ROWS PER MATCH WITH UNMATCHED ROWS
PATTERN ( a{3,})
DEFINE a AS FLAG_1 = 1
) mr
GROUP BY CUSTOMER_ID;
Output:
The power of this solution lies at the PATTERN part which could be easily extended with new conditions. For instance:
PATTERN ( a b{1,2} a )
DEFINE a AS FLAG_1 = 1,
b AS FLAT_2 = 0;
Here: Find sequence of flag = 1, followed by one or two occurences of flag = 0 and ended by flag = 1.