如何在MySQL中执行"水平UNION"？(结表)

Question

我正在寻找连接或联合两个(或更多)表的可能性.我无法加入所有表,因为没有引用没有匹配的列.如果我在没有任何"开启"的情况下加入,我将从表1中获得所有数据乘以表2中的所有数据(不是我想要的).所以我试图提供带有MySQL用户定义变量的假rownums,但由于所有表中都有不同数量的数据,我无法对其进行比较.这有点难以解释.所以我将提供一些例子.

例1(表1 = 4行,表2 = 3行,结果= 4行)

+---------+---------+---------------+
| Table 1 | Table 2 | Result        |
+---------+---------+-------+-------+
| Col 1   | Col 1   | Col 1 | Col 2 |
+---------+---------+-------+-------+
| A       | H       | A     | H     |
| B       | I       | B     | I     |
| C       | J       | C     | J     |
| D       |         | D     | NULL  |
+---------+---------+-------+-------+

例2(表1 = 3行,表2 = 4行,结果= 4行)

+---------+---------+---------------+
| Table 1 | Table 2 | Result        |
+---------+---------+-------+-------+
| Col 1   | Col 1   | Col 1 | Col 2 |
+---------+---------+-------+-------+
| A       | H       | A     | H     |
| B       | I       | B     | I     |
| C       | J       | C     | J     |
|         | K       | NULL  | K     |
+---------+---------+-------+-------+

例3(表1 = 3行,表2 = 4行,表3 = 2行,结果= 4行)

+---------+---------+---------+-----------------------+
| Table 1 | Table 2 | Table 3 | Result                |
+---------+---------+---------+-------+-------+-------+
| Col 1   | Col 1   | Col 1   | Col 1 | Col 2 | Col 3 |
+---------+---------+---------+-------+-------+-------+
| A       | H       | O       | A     | H     | O     |
| B       | I       | P       | B     | I     | P     |
| C       | J       |         | C     | J     | NULL  |
|         | K       |         | NULL  | K     | NULL  |
+---------+---------+---------+-------+-------+-------+

现在是真正的困难部分.我需要这个作为查询.我不想填写其他临时表.如果可能的话 :-)

Answer 1

我认为你加入了每个表的密集顺序等级,只是按"Col 1"值排序？

这实际上是每个表的等级的完全外连接.

不幸的是,MySQL不支持ROW_NUMBER()分析函数,这会使这个相对简单:

SELECT *
FROM (SELECT "Col 1", ROW_NUMBER() (OVER ORDER BY "Col 1") AS RowNum FROM "Table 1") AS T1
FULL OUTER JOIN (SELECT "Col 1", ROW_NUMBER() (OVER ORDER BY "Col 1") AS RowNum FROM "Table 2") AS T2
    ON T2.RowNum = T1.RowNum
FULL OUTER JOIN (SELECT "Col 1", ROW_NUMBER() (OVER ORDER BY "Col 1") AS RowNum FROM "Table 3") AS T3
    ON T3.RowNum = T2.RowNum
ORDER BY COALESCE(T1.RowNum, T2.RowNum, T3.RowNum)

MySQL中有其他选择,但我不熟悉这些解决方法.

至于FULL OUTER JOIN解决方法,它很容易排名,因为已知的排名只是自然数:

SELECT *
FROM Numbers
LEFT JOIN (SELECT "Col 1", ROW_NUMBER() (OVER ORDER BY "Col 1") AS RowNum FROM "Table 1") AS T1
    ON T1.RowNum = Numbers.Number
LEFT JOIN (SELECT "Col 1", ROW_NUMBER() (OVER ORDER BY "Col 1") AS RowNum FROM "Table 2") AS T2
    ON T2.RowNum = Numbers.Number
LEFT JOIN (SELECT "Col 1", ROW_NUMBER() (OVER ORDER BY "Col 1") AS RowNum FROM "Table 3") AS T3
    ON T2.RowNum = Numbers.Number
WHERE COALESCE(T1.RowNum, T2.RowNum, T3.RowNum) IS NOT NULL
ORDER BY Numbers.Number