如何获取列的 n 个不同值的行

Question

我需要获取 n 个不同发票编号的行。

我有 SELECT 查询，它可以从表中得到结果：

SELECT A.INVOICE_NUMBER, A.INVOICE_SEQ_NUMBER, B.FILE_NUMBER 
FROM TABLE1 AS A, TABLE2 AS B 
WHERE A.INVOICE_NUMBER = B.INVOICE_NUMBER 
      AND A.INVOICE_SEQ_NUMBER = B.INVOICE_SEQ_NUMBER

所以我得到这个作为我的查询的结果：

-----------------------------------------------------
| INVOICE_NUMBER | INVOICE_SEQ_NUMBER | FILE_NUMBER |
------------------------------------------------------
|1111111111-1    |          1         | P4324324525 |
-----------------------------------------------------
|1111111111-1    |          2         | P4565674574 |
-----------------------------------------------------
|1111111111-1    |          3         | V4324552557 |
-----------------------------------------------------
|1111111111-1    |          4         | V4324552525 |
-----------------------------------------------------
|2222222222-2    |          1         | S4563636574 |
-----------------------------------------------------
|3333333333-3    |          1         | Q4324325675 |
-----------------------------------------------------
|3333333333-3    |          2         | Q4565674574 |
-----------------------------------------------------
|4444444444-4    |          1         | F4326364366 |
-----------------------------------------------------
|4444444444-4    |          2         | F4565636323 |
-----------------------------------------------------
|4444444444-4    |          3         | F4398798588 |
-----------------------------------------------------
|4444444444-4    |          4         | F4565865888 |
-----------------------------------------------------

但我需要的是，例如，只获得三个不同发票号码的结果，所以我的查询应该给出这个：

-----------------------------------------------------
| INVOICE_NUMBER | INVOICE_SEQ_NUMBER | FILE_NUMBER |
------------------------------------------------------
|1111111111-1    |          1         | P4324324525 |
-----------------------------------------------------
|1111111111-1    |          2         | P4565674574 |
-----------------------------------------------------
|1111111111-1    |          3         | V4324552557 |
-----------------------------------------------------
|1111111111-1    |          4         | V4324552525 |
-----------------------------------------------------
|2222222222-2    |          1         | S4563636574 |
-----------------------------------------------------
|3333333333-3    |          1         | Q4324325675 |
-----------------------------------------------------
|3333333333-3    |          2         | Q4565674574 |
-----------------------------------------------------

我怎样才能实现它？

Answer 1

你听说过JOIN吗？

无论如何，解决问题的一种方法是使用DENSE_RANK()：

SELECT INVOICE_NUMBER, INVOICE_SEQ_NUMBER, FILE_NUMBER
FROM (SELECT A.INVOICE_NUMBER, A.INVOICE_SEQ_NUMBER, B.FILE_NUMBER,
             DENSE_RANK() OVER (ORDER BY A.INVOICE_NUMBER) as seqnum
      FROM TABLE1 A JOIN
           TABLE2 B 
           ON A.INVOICE_NUMBER = B.INVOICE_NUMBER AND 
              A.INVOICE_SEQ_NUMBER = B.INVOICE_SEQ_NUMBER
     ) t
WHERE seqnum <= 3;