android - 如何在 sqlite 中将 2 列组合成一个新列

Question

我有一个包含 3 列的表格，我必须将 2 列中的值按降序排列成一列。

+---+---+---+| A | B | C |+---+---+---+    | z | 1 | 2 |  | f | 5 | 7 | | s | 9 | 5 |+---+---+---+

Using this example the output would be putting the values from column B and C into one like this:

+---+----+| A | B  |+---+----+ | s | 9  || f | 7  || f | 5  || s | 5  | | z | 2  || z | 1  |+---+----+

My current code:

 String SELECT_QUERY = "SELECT a, b, c AS b FROM _table ORDER BY b DESC" ;

我该怎么做？谢谢。

Answer 1

首先使用 UNION 组合两个查询，然后对组合结果进行降序排序。

查询

 SELECT * FROM
 (
     SELECT A,B
     FROM tbl
     UNION
     SELECT A,C
     FROM tbl
 )t
 ORDER BY t.B DESC;

在你的情况下，

String SELECT_QUERY = "SELECT * FROM (SELECT A,B FROM _table UNION SELECT A,C FROM _table)t ORDER BY t.B DESC" ;

Fiddle demo for your reference

截图

希望这对您有所帮助。