mysql - 当外键相似时如何获取单行

Question

我有一个包含列的表 tbl_issue

> serial_no.
 Issue_no. (f.k) 
From_Section 
To_Section
+-----+---------------+-------------+-------------+
| id  | issue no      | from section| to_section  |
+-----+---------------+-------------+-------------+
| 1   | 223           |   MFA       | N/A         |
| 2   | 223           |   N/A       | LOG         |
+----------+----------+-------------+--------------+

当我查询第 1 期的表时。我得到两行，任何人都可以帮助我如何获得一条记录并且没有“N/A”

Answer 1

对于您给出的示例，这可行:

WITH combined AS
(
SELECT    i.issue_no,
          CASE WHEN i.from_section = 'N/A' THEN i2.from_section ELSE i.from_section END from_section,
          CASE WHEN i.to_section = 'N/A' THEN i2.to_section ELSE i.to_section END to_section
FROM          dbo.tbl_issue i
INNER JOIN  dbo.tbl_issue i2
    ON    i2.issue_no = i.issue_no
)

SELECT    DISTINCT *
FROM          combined c
WHERE     c.from_section <> 'N/A' AND c.to_section <> 'N/A'

假设“N/A”并不意味着 NULL...如果您的意思是 NULL，请将“= 'N/A'”替换为 IS NULL，并将“<> 'N/A'”替换为 IS不为空