SQL查询：使用内部联接对结果行进行附加筛选

Question

Given Table_1:

| testing | main_val |
| AB      | VAL      |
| EF      | DIP      |

and Table_2:

| main_val | for_testing |
| VAL      |             |
| VAL      | AB          |
| VAL      | CD          |
| DIP      |             |
| DIP      | GH          |

My join query is below:

select table1.testing, table1.main_val, table2.for_testing from table_1 table1
inner join table_2 table2 on table1.main_val = table2.main_val

I get the following result:

| testing | main_val | for_testing |
| AB      | VAL      |             |
| AB      | VAL      | AB          |
| AB      | VAL      | CD          |
| EF      | DIP      |             |
| EF      | DIP      | GH          |

My requirement is to get the best "testing match". If the testing and for_testing columns match, then I should retrieve that row. If no matches, choose the empty for_testing row. I need the result to look like:

| testing | main_val | for_testing |
| AB      | VAL      | AB          |
| EF      | DIP      |             |

More columns will be added for this join, that is why getting the best match row is important.

Answer 1

Try this:

select table1.testing, table1.main_val, table2.for_testing 
from table_1 table1
inner join table_2 table2 on table1.main_val = table2.main_val 
where table1.testing =table2.for_testing 
union 
select table1.testing, table1.main_val, table2.for_testing 
from table_1 table1
inner join table_2 table2 on table1.main_val = table2.main_val 
where not in (select table1.testing, table1.main_val, table2.for_testing 
from table_1 table1
inner join table_2 table2 on table1.main_val = table2.main_val 
where table1.testing =table2.for_testing ) and t2.for_testing =""

Answer 2

Try this:

;WITH CTE AS(
    SELECT 
        t1.*,
        t2.For_Testing,
        RN = ROW_NUMBER() 
                OVER(
                    PARTITION BY t1.Main_Val 
                    ORDER BY 
                        CASE 
                            WHEN t1.Testing = t2.For_Testing THEN 1
                            WHEN t2.For_Testing = '' THEN 2
                            ELSE 999
                        END
                    )
    FROM Table_1 t1
    INNER JOIN Table_2 t2
        ON t2.MAIN_val = t1.Main_Val
)
SELECT
    Testing,
    Main_val,
    For_Testing
FROM CTE
WHERE RN = 1
ORDER BY Testing

Answer 3

您必须使用Left Join并在加入时添加for_testing。

Answer 4

Try this...

This is work for me

select Table_1.testing,Table_1.main_val,Table_2.for_testing from Table_2 right join

 Table_1 on Table_2.main_val=Table_1.main_val and Table_2.for_testing=Table_1.testing

Answer 5

Try this:-

SELECT table1.testing, table1.main_val, table2.for_testing 
FROM table_1 table1 INNER JOIN table_2 table2 
ON table1.main_val = table2.main_val
WHERE table1.testing = table2.for_testing
OR table1.testing IS NULL;

I think this can help you.