Join two columns and pick just one from the child results - sql-server

Question

I want to perform a JOIN on two tables to get the LEADTIME per ITEMNUM.
Both tables have common value ITEMNUM that I use for the JOIN operation.
The problem is that in the second table the ITEMNUM is not unique and can contain multiple. different LEADTIME values.
For example see ITEMNUM 2 in Table 2.
In case there are multiple LEADTIME values, I just want to get one of the LEADTIME values.
I don't care which one.
This is what I have so far, but it keeps returning multiple lines for ITEMNUM 2
SELECT ITEMNUM, LEADTIME
FROM TABLE1
LEFT JOIN TABLE2 on TABLE2.ITEMNUM = TABLE1.ITEMNUM
So what can I do to get just one LEADTIME for ITEMNUM 2? ( as mentioned, I don't care which value )

Answer 1

This approach assigns a row number to each row in #table2 resetting it for each ItemNum value. You need to have an order by clause (if you don't SQL Server raises an error) so I am ordering by NEWID() which should result in a randomized order. You will likely want to tweak what columns you are returning. Here is the dbfiddle to see it in action.
IF OBJECT_ID('tempdb.dbo.#table1', 'U') IS NOT NULL DROP TABLE #table1;
IF OBJECT_ID('tempdb.dbo.#table2', 'U') IS NOT NULL DROP TABLE #table2;
CREATE TABLE #table1
(
ID INT
, ItemNum INT
);
CREATE TABLE #table2
(
ID INT
, ItemNum INT
, LeadTime INT
);
INSERT INTO #table1 VALUES (1, 1)
INSERT INTO #table1 VALUES (2, 2)
INSERT INTO #table1 VALUES (3, 3)
INSERT INTO #table1 VALUES (4, 4)
INSERT INTO #table1 VALUES (5, 5)
INSERT INTO #table2 VALUES (1, 1, 6)
INSERT INTO #table2 VALUES (2, 2, 7)
INSERT INTO #table2 VALUES (3, 2, 2)
INSERT INTO #table2 VALUES (4, 3, 6)
INSERT INTO #table2 VALUES (5, 4, 3)
SELECT *
FROM #table1 AS t1
LEFT JOIN (
SELECT *
, ROW_NUMBER() OVER (PARTITION BY ItemNum ORDER BY NEWID()) AS rn
FROM #table2
) AS t2 ON t1.ItemNum = t2.ItemNum
AND t2.rn = 1;

Answer 2

There are several ways to get this done.I would use OUTER APPLY with TOP.
DROP TABLE IF EXISTS #Table1
CREATE TABLE #Table1
(
Id INT
, ItemNum INT
)
DROP TABLE IF EXISTS #Table2
CREATE TABLE #Table2
(
Id INT
, ItemNum INT
, LeadTime INT
)
INSERT INTO #Table1 VALUES
(1, 1)
, (2, 2)
, (3, 3)
, (4, 4)
, (5, 5)
INSERT INTO #Table2 VALUES
(1, 1, 6)
, (2, 2, 7)
, (3, 2, 2)
, (4, 3, 6)
, (5, 4, 3)
SELECT
*
FROM
#Table1 AS T1
OUTER APPLY
(
SELECT TOP 1 T2.LeadTime FROM #Table2 AS T2 WHERE T2.ItemNum = T1.ItemNum
) AS LT