Question

有一个退货样本：

  id | value1 | value2
-------------------------
   1 |  AAAA  |  NULL
   2 |  NULL  |  BBBB
   3 |  CCCC  |  DDDD

需要得到它：

  id | value 
--------------
   1 |  AAAA  
   2 |  BBBB  
   3 |  CCCC  
   3 |  DDDD

作为sql的一种方式我明白了吗？

Answer 1

尝试这样的事情

select Id, value1 from yourtable
Where value1 is not null
Union all
select Id, value2 from yourtable
Where value2 is not null

Answer 2

它应该与UNION：

一起使用

SELECT col1, col2 FROM table WHERE col2 IS NOT NULL
UNION
SELECT col3, col4 FROM table WHERE col4 IS NOT NULL

如果要保留重复项，请使用UNION ALL

Answer 3

您可以尝试这样的事情

insert into #temp (id, value1, value2) values
(1,'AAAA', NULL)
,(2,NULL,'BBBB')
,(3, 'CCCC','DDDD')

select id, value1 as value from #temp where value1 is not null
union all
select id, value2 as value from #temp where value2 is not null

Answer 4

这对于mysql IFNULL和sql-server ISNULL也很有帮助。

SELECT id, IFNULL(value1, value2) val1 FROM table1 
UNION ALL
SELECT id, value2 FROM table1 WHERE value1 IS NOT NULL AND value2 IS NOT NULL

SQL联合字段合二为一

4 个答案: