是否可以将一个表连接到另一个表，而第一个表中的一个列与第二个表中的多个列之一匹配？

Question

I have a SQL database with two tables, People and Itinerary .

People table columns:

• ...
• Item1
• Item2
• Item3
• ...

Itinerary table columns:

• ID
• COLUMN2
• ...

In the people table, the columns Item1 , Item2 , and Item3 match values in the ID column for some row in the Itinerary table.

Is it possible to join the itinerary table to all three Item_ columns? Eg, something like the following:

SELECT DISTINCT Itinerary.COLUMN2
FROM    People
        JOIN Itinerary ON People.ITEM1 = Itinerary.ID
        JOIN Itinerary ON People.ITEM2 = Itinerary.ID
        JOIN Itinerary ON People.ITEM3 = Itinerary.ID

Note that the above query doesn't work.

Answer 1

You can do what you want by using or or in in the on clause:

SELECT DISTINCT ITINERARY.COLUMN2
FROM People pl JOIN
     Itinerary i
     ON i.ID IN (pl.ITEM1, pl.ITEM2, pl.ITEM3)

Answer 2

I'm not sure I understand your question entirely, but maybe something like this?

SELECT DISTINCT Itinerary.COLUMN2

FROM People
    LEFT OUTER JOIN Itinerary ON
    (
        Itinerary.ID = People.ITEM1
        OR Itinerary.ID = People.ITEM2
        OR Itinerary.ID = People.ITEM3
    )