SQL Server：从第一个表链接到第二个表的主键的多个外键

Question

I have two tables, itemrequest_table and item_table . Four columns of itemrequest_table ( item1, item2, item3, item4 ) are connected to item_no of item_table .

I'm trying to write a query to display the item names of item_nos under the column of item1, item2, item3, item4.

But how can I display the item names it? And is it possible to query that?

My tables:

Answer 1

You just need to do four joins between the two tables - one for each item:

SELECT
   Item1 = i1.item_name,    
   Item2 = i2.item_name,
   Item3 = i3.item_name,
   Item4 = i4.item_name
FROM
   itemrequest_table ir
INNER JOIN
   item_table i1 ON ir.item1 = i1.item_no
INNER JOIN
   item_table i2 ON ir.item2 = i2.item_no
INNER JOI
   item_table i3 ON ir.item3 = i3.item_no
INNER JOIN
   item_table i4 ON ir.item4 = i4.item_no       

But this is really a bad design - it smells of first-normal form violation ( repeating columns ). What you really should do is just have a relationship between itemrequest_table and the item_table that allows for any number of connections, if needed (a regular, normal m:n relationship)

Answer 2

You need to perform four joins:

SELECT    ir.request_no, 
          t1.item_name, t2.item_name, t3.item_name, t4.item_name
FROM      itemrequest_table ir
LEFT JOIN item_table t1 ON ir.item1 = t1.item_no
LEFT JOIN item_table t2 ON ir.item2 = t2.item_no
LEFT JOIN item_table t3 ON ir.item3 = t3.item_no
LEFT JOIN item_table t4 ON ir.item4 = t4.item_no

EDIT:
As per the comments, these items are optional, so a left join should be used instead of a join .