Question

我在sql数据库中有三个表

我需要加入这三个表来获得这样的表

我想加入三个表来获取整个第一，第三和第二（其中sort为2）表的所有数据

我尝试这个查询

  select table1.Item, table1.Location, table1.Type,
         table2.Item, table2.Location, table2.Type,table2.Sort
         table3.Item, table3.Location, table3.Type
   from table1
 full outer join table2
  on table1.Item = table2.Item
  and table1.Location = table2.Location
  and table1.Type = table2.Type
  and table2.Sort = '2'
 full outer join table3
  on table1.Item = table3.Item
  and table1.Location = table3.Location
  and table1.Type = table3.Type

但我只得到这张表

如何使用所有组合进行查询以获得我想要的表格？

有什么想法吗？

Answer 1

您的方法是正确的，您所缺少的就是在第二个加入标准中使用coalesce。

第一个outer join会返回一组包含null个值的行，如果您在第三个join个标准中使用这些值，则该条件不会满意。

您可以使用coalesce解决此问题，如果第一个参数为null

，则会使用第二个参数

select  table1.Item, table1.Location, table1.Type,
        table2.Item, table2.Location, table2.Type,table2.Sort
        table3.Item, table3.Location, table3.Type
from    table1
full outer join table2
on      table1.Item = table2.Item and
        table1.Location = table2.Location and
        table1.Type = table2.Type
full outer join table3
on      coalesce(table1.Item, table2.Item) = table3.Item and
        coalesce(table1.Location, table2.Location) = table3.Location and
        coalesce(table1.Type, table2.Type) = table3.Type
where   coalesce(table2.Sort, 2) = 2

Answer 2

select table1.Item, table1.Location, table1.Type,
       table2.Item, table2.Location, table2.Type, table2.Sort,
       table3.Item, table3.Location, table3.Type
from table1
  full outer join table3
    on  table1.Item = table3.Item
   and table1.Location = table3.Location
   and table1.Type = table3.Type
  full outer join table2
    on (table1.Item = table2.Item
   and table1.Location = table2.Location
   and table1.Type = table2.Type
   and table2.Sort = '2'
   )
   or (table3.Item = table2.Item
   and table3.Location = table2.Location
   and table3.Type = table2.Type
   and table2.Sort = '2'
   )
where (table2.Sort = '2' or table2.Sort is null)

rextester演示：http://rextester.com/MNW25175

结果

+------+----------+-------+------+----------+-------+------+------+----------+-------+
| Item | Location | Type  | Item | Location | Type  | Sort | Item | Location | Type  |
+------+----------+-------+------+----------+-------+------+------+----------+-------+
| 123  | A        | small | NULL | NULL     | NULL  | NULL | 123  | A        | small |
| NULL | NULL     | NULL  | 123  | A        | big   | 2    | 123  | A        | big   |
| NULL | NULL     | NULL  | 123  | B        | small | 2    | NULL | NULL     | NULL  |
+------+----------+-------+------+----------+-------+------+------+----------+-------+

这也有效，但只是因为table2与table1中的所有行匹配，这可能不符合您的实际用例：

select table1.Item, table1.Location, table1.Type,
       table2.Item, table2.Location, table2.Type, table2.Sort,
       table3.Item, table3.Location, table3.Type
from table1
  full outer join table3
    on  table1.Item = table3.Item
   and table1.Location = table3.Location
   and table1.Type = table3.Type
  full outer join table2
    on table3.Item = table2.Item
   and table3.Location = table2.Location
   and table3.Type = table2.Type
   and table2.Sort = '2'
where (table2.Sort = '2' or table2.Sort is null)

Answer 3

使用LEFT OUTER JOIN：

 SELECT *  FROM Table 2 
 LEFT OUTER JOIN Table 1 ON table1.Item = table2.Item AND  table1.Location =  
                  table2.Location AND table1.Type = table2.Type and 
                  table2.Sort = '2'
 LEFT OUTER JOIN Table 3 ON table1.Item = table3.Item
                 and table1.Location = table3.Location
                 and table1.Type = table3.Type

Answer 4

您可以通过以下查询获得所需的结果

SELECT d.item, d.location, d.[type],
    s.item, s.location, s.[type], s.sort,
    h.item, h.location, h.[type]
FROM tblData d
    FULL OUTER JOIN tblSearchData s
        ON d.item = s.item 
        AND d.location = s.location
        AND d.[type] = s.[type]
    FULL OUTER JOIN tblHelpData h
        ON (s.item = h.item OR d.item=h.item)
        AND (s.location = h.location OR d.location=h.location)
        AND (s.[type] = h.[type] OR d.[type]=h.[type])
WHERE s.sort=2 OR s.sort IS NULL

SQL - 完全外连接

4 个答案: