我有一个表格table_One
,其中有多个columns(Column1, Column2, Column3, Column4.....)
引用(Contains PK values for Table_two
)到另一个表Table_Two
。是否有任何有效的方法来加入这两个表而不是将Table_one连接回table_Two Multiple Times.br/>
两个表的结构和期望的结果集如下。 Table_One
答案 0 :(得分:2)
您是否尝试过对table2表进行别名并将其连接到Table_One两次,如下所示?
SELECT
t1.PrimaryKey,
c1.ColumnA AS Column1,
c2.ColumnA AS Column2
FROM Table_One t1
JOIN Table_two c1 ON t1.Column1 = c1.ID
JOIN Table_two c2 ON t1.Column2 = c2.ID;
答案 1 :(得分:1)
Select Table_One.PrimaryKey,
T2_Column1.ColumnA As Column1,
T2_Column2.ColumnA As Column2
From Table_One
Inner Join Table_Two As T2_Column1
On Table_One.Column1 = T2_Column1.ID
Inner Join Table_Two As T2_Column2
On Table_One.Column2 = T2_Column2.Id
基本上,你加入表2两次。当你这样做时,你必须至少其中一个别名,以便SQL不会混淆。作为一种惯例,通常最好对两者进行别名,这样当您在6个月内再次阅读此代码时,它将更容易理解。
答案 2 :(得分:1)
以下解决方案(SQLFiddle)只读取第二个表中的行:
SET STATISTICS IO ON;
...
PRINT 'Test #1'
SELECT *
FROM
(
SELECT ca.PrimaryKey, ca.[Type], y.ColumnA
FROM @Table1 x
UNPIVOT( Value FOR [Type] IN ([Column1], [Column2]) ) ca
INNER MERGE /*HASH*/ JOIN @Table2 y ON ca.Value = y.ID
) src
PIVOT( MAX(src.ColumnA) FOR src.[Type] IN ([Column1], [Column2]) ) pvt
PRINT 'End of Test #1'
结果:
Test #1
PrimaryKey Column1 Column2
---------- --------- -------
1 ALPHA CHARLIE
2 BETA DELTA
3 CHARLIE ALPHA
4 DELTA CHARLIE
5 ALPHA DELTA
6 CHARLIE ALPHA
7 ALPHA DELTA
8 DELTA CHARLIE
Table 'Worktable'. Scan count 0, logical reads 0, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table '#65B6F546'. Scan count 1, logical reads 2, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table '#61E66462'. Scan count 1, logical reads 2, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
End of Test #1