Question

我有1个包含3列的表。 id（auto_increment），column0，column1如下：

+----+--------+---------+
| id | column0| column1 |
+----+--------+---------+
| 1  | 1.1111 | 0.1111  |
| 2  | 1.2222 | 0.2222  |
| 3  | 1.3333 | 0.3333  |
| 4  | 1.4444 | 0.4444  |
| .  | 1.5555 | 0.5555  |
+----+--------+---------+

我想选择这个：

+--------+---------+
| column0| column1 |
+--------+---------+
| 1.1111 | 0.2222  |
| 1.2222 | 0.3333  |
| 1.3333 | 0.4444  |
| 1.4444 | 0.5555  |
| 1.5555 | 0.5555  |
+--------+---------+

如何将这两个查询连接到一个查询中？有人可以为我编写代码。

SELECT column0 FROM table;

和第二个查询

SELECT column1 FROM table where id >1
union all
(SELECT column1 FROM table
ORDER BY id DESC 1);

Answer 1

使用自我加入

SELECT t1.column0, IFNULL(t2.column1, t1.column1) AS column1
FROM table AS t1
LEFT JOIN table AS t2 ON t1.id = t2.id - 1

处理最后一行需要LEFT JOIN和IFNULL。你也可以用UNION

来做

SELECT t1.column0, t2.column1
FROM table AS t1
INNER JOIN table AS t2 ON t1.id = t2.id - 1
UNION
(SELECT column0, column1
 FROM table
 ORDER BY id DESC
 LIMIT 1)

DEMO

请注意，这只适用于id序列中没有间隙的情况。当存在间隙时找到下一行更复杂。您可以搜索SO以获取显示如何执行此操作的解决方案。

Answer 2

如果我正确地关注你，你想要将column0或下一行的一行和一列作为单个记录返回，但除了逻辑“下一个排序的行”之外，没有链接它们的“键”。 / p>

如果这是正确的，请尝试这个。

select t1.column0, t2.column1 from
(select @t1row := @t1row + 1 as t1row, x1.column0 from (select @t1row := 0) as r1, tablex as x1 order by id) as t1,
(select @t2row := @t2row + 1 as t2row, x2.column1 from (select @t2row := 0) as r2, tablex as x2 where x2.id != (select min(x3.id) from tablex as x3) order by id) as t2
where t1.t1row = t2.t2row;

这应该返回：

column0 column1
1.1111  0.2222
1.2222  0.3333
1.3333  0.4444
1.4444  0.5555

但是这使得我们没有“最后”行的第0列和“第一”行的第1列。处理基于您想要完成的事情。 1）不要包括它们 2）再返回一行，将last.column0与first.column1连接起来 3）返回一行，其中last.column0链接到空列1，另一行返回空列column0链接到first.column1

如果＃1，你实际上已经完成了。

如果是＃2，请将此union子句添加到上面的查询中：

union
select x1.column0, x2.column1
from tablex as x1, tablex as x2, (select min(xi.id) as minid, max(xi.id) as maxid from tablex as xi) as x3
where x1.id = x3.maxid and x2.id = x3.minid

你得到：

column0 column1
1.1111  0.2222
1.2222  0.3333
1.3333  0.4444
1.4444  0.5555
1.5555  0.1111

如果是＃3，请将这些union子句添加到上面的查询中：

union
select x1.column0, null as column1 from tablex as x1 where x1.id = (select max(xi.id) from tablex as xi)
union
select null as column0, x2.column1 from tablex as x2 where x2.id = (select min(xi.id) from tablex as xi)

你得到了（你可以随意使用它们）：

column0 column1
1.1111  0.2222
1.2222  0.3333
1.3333  0.4444
1.4444  0.5555
1.5555
        0.1111

享受！

如何编写简单的MySQL工作台查询

2 个答案: