SQL get only earlier date in repetitive rows - mysql

Question

I have an SQL table contains transactions like this
ID | FK | STATUS | DATE
1 | A | K1 | 2021-01-01
2 | A | K1 | 2021-01-15
3 | A | K2 | 2021-01-30
4 | A | K2 | 2021-02-03
5 | B | K1 | 2021-01-12
6 | C | K1 | 2021-03-30
7 | C | K3 | 2021-09-15
As we can see, some FK have some records with different STATUS and different DATE. From each FK I want to get the first/earlier transaction date with status K1.
Maybe something like this.
ID | FK | STATUS | DATE
1 | A | K1 | 2021-01-01
5 | B | K1 | 2021-01-12
6 | C | K1 | 2021-03-30
How can I get the result like that?
Note : I'm using MariaDB version 10.5.9-MariaDB

Answer 1

CREATE TABLE my_table (
`ID` INTEGER,
`FK` VARCHAR(1),
`STATUS` VARCHAR(2),
`DATE` DATETIME
);
INSERT INTO my_table
(`ID`, `FK`, `STATUS`, `DATE`)
VALUES
('1', 'A', 'K1', '2021-01-01'),
('2', 'A', 'K1', '2021-01-15'),
('3', 'A', 'K2', '2021-01-30'),
('4', 'A', 'K2', '2021-02-03'),
('5', 'B', 'K1', '2021-01-12'),
('6', 'C', 'K1', '2021-03-30'),
('7', 'C', 'K3', '2021-09-15');
Query #1
SELECT
ID,
FK,
STATUS,
DATE
FROM (
SELECT
*,
row_number() over (partition by FK,STATUS order by DATE ASC) rn from my_table
) t
where STATUS='K1' and rn=1;
ID
FK
STATUS
DATE
1
A
K1
2021-01-01 00:00:00
5
B
K1
2021-01-12 00:00:00
6
C
K1
2021-03-30 00:00:00
View on DB Fiddle

Answer 2

WITH cte_customers AS (
SELECT
ROW_NUMBER() OVER(PARTITION BY fk,status
ORDER BY
date
) row_num,
customer_id,
fk,
status
FROM
sales.customers
) SELECT
*
FROM
cte_customers
WHERE
row_num =1;

Answer 3

This is solved with a windowing function:
WITH RowNumbers AS (
SELECT *,
row_number() OVER (PARTITION BY FK ORDER BY Date) As rn
FROM [MyTable]
WHERE Status = 'K1'
)
SELECT ID, FK, STATUS, DATE
FROM RowNumbers
WHERE rn = 1
Window functions were added to MariaDB in version 10.2. The CTE is also needed because row_number() isn't computed until after the WHERE clause is processed.