Question

所以我遇到了从查询中获取正确数据的问题。

我有下表（人）：

Name  |       xpath        |   value
Derek |  /body/torso/arm   |   left
Derek |  /body/torso/arm   |   right
Derek |  /body/torso/neck  |   Head
Ron   |  /body/torso/neck  |   Head
Ron   |  /body/torso/arm   |   left

所以基本上我试图得到的查询结果是显示差异（这两个人之间缺少什么）。

results:
Name1 |       xpath1       |   value1   | Name2  |   xpath2         |   value2
Derek |  /body/torso/arm   |   right    | Ron    |    NULL          |   NULL

我甚至可以获得以下回复

results:
Name1 |       xpath1       |   value1   | Name2  |   xpath2         |   value2
Derek |  /body/torso/arm   |   right    | Ron    |    NULL          |   NULL
Derek |  /body/torso/arm   |   left     | Ron    | /body/torso/arm  |   left  
Derek |  /body/torso/neck  |   Head     | Ron    | /body/torso/neck |   Head

我正在使用的查询是：

SELECT P.Name , P.xpath, P.value, P1.Name, P2.xpath, P3.value
FROM Person as P
LEFT OUTER JOIN
    Person as P2 ON P.xpath = P2.xpath
WHERE
         P.Name = "Derek"
    AND  P2.Name = "Ron"

无论我尝试什么，我一直得到的结果基本上是重叠的数据，但从来没有我真正想要的东西，似乎我错过了一些简单或明显做错的事情。有什么建议？最终我将在SPROC中运行它，但能够处理多个名称而不仅仅是2，但如果我有，Derek，Ron，John，Dawn等等将是很好的。

Answer 1

试一试：

SELECT    a.Name  AS Name1,
          a.xpath AS xpath1,
          a.value AS value1,
          'Ron'   AS Name2,
          b.xpath AS xpath2,
          b.value AS value2
FROM      Person a
LEFT JOIN Person b ON b.Name = 'Ron'
                  AND a.xpath = b.xpath 
                  AND a.value = b.value
WHERE     a.Name = 'Derek' AND
          b.Name IS NULL

SQLFiddle Demo

如果您想将Derek与多个名称进行比较，您可以对要比较的所有名称CROSS JOIN进行比较（以便名称可以显示在结果集中），并LEFT JOIN使用相同的表格使用xpath，value以及CROSS JOIN中指定的姓名：

SELECT     a.Name  AS Name1,
           a.xpath AS xpath1,
           a.value AS value1,
           b.Name  AS Name2,
           c.xpath AS xpath2,
           c.value AS value2
FROM       Person a
CROSS JOIN (
           SELECT 'Ron' AS Name UNION ALL
           SELECT 'John'        UNION ALL
           SELECT 'Charles'     UNION ALL
           SELECT 'Aaron'
           ) b
LEFT JOIN  Person c ON b.Name  = c.Name 
                   AND a.xpath = c.xpath
                   AND a.value = c.value
WHERE      a.Name = 'Derek' AND
           c.Name IS NULL

SQLFiddle Demo

如果你想在比较的左边有多个名字（不仅仅是“Derek”），那就改变

a.Name = 'Derek'

到

a.Name <> b.Name

在上面的查询中。

SQLFiddle Demo

编辑：只是为了更进一步：

将所有名称与所有名称进行比较：

SELECT     a.Name  AS Name1,
           a.xpath AS xpath1,
           a.value AS value1,
           b.Name  AS Name2,
           c.xpath AS xpath2,
           c.value AS value2
FROM       Person a
CROSS JOIN (SELECT DISTINCT Name FROM Person) b
LEFT JOIN  Person c ON b.Name  = c.Name 
                   AND a.xpath = c.xpath
                   AND a.value = c.value
WHERE      a.Name <> b.Name AND 
           c.Name IS NULL

Answer 2

尝试使用EXCEPT联盟：</ p>

WITH tbl (name, xpath, value) as
    (values
        ('Derek','/body/torso/arm','left'),
        ('Derek','/body/torso/arm','right'),
        ('Derek','/body/torso/neck','Head'),
        ('Ron','/body/torso/neck','Head'),
        ('Ron','/body/torso/arm','left')
    )
SELECT xpath, value 
FROM tbl 
WHERE name = 'Derek'
    EXCEPT
        SELECT xpath, value 
        FROM tbl 
        WHERE name = 'Ron'

查询以查找同一表中的差异

2 个答案: