SQL Duplicate Values Issue on LEFT OUTER JOIN - sql

Question

I am trying to do a Join within 4 tables but it is returning duplicate rows. Some Items might not exist on Sales and Inventory tables. What needs to be done to resolve the issue;
ProductList (We need all the items)
Item_ID
ProductDetail (it has the return all the matching items from Product List)
Item_ID
Product_Name
Sales (needs to return all matching items from ProductList)
Item_ID
Sales_Qty
Inventory
Item_ID
Remaining_Qty
SAMPLE DATA
ProductList
Item_Id
--------
0001
0002
0003
0004
ProductDetail
Item_Id Product_Name
-----------------------
0001 Eraser
0002 Pencil
0003 Pen
0004 Mouse
0005 Keyboard
0006 Monitor
0007 Cable
Sales
Item_ID Sales_Qty
--------------------
0001 15
0002 20
0004 50
0005 60
0006 45
Inventory
Item_ID Remaining
-------------------
0001 100
0002 95
0003 55
0005 101
0006 13
0007 18
Desired output:
Item_Id Item_Name Sales_Qty Remaining_Qty
--------------------------------------------------
0001 Eraser 15 100
0002 Pencil 20 95
0003 Pen 0 55
0004 Mouse 50 0
My query :
SELECT *
FROM ProductList a
INNER JOIN ProductDetail b ON a.Item_ID = b.ItemID
LEFT JOIN Sales c ON a.Item_Id = c.Item_ID
LEFT JOIN Inventory d ON a.Item_ID = d.Item_ID

Answer 1

You can use DISTINCT
SELECT DISTINCT a.Item_ID, *
FROM ProductList a
INNER JOIN ProductDetail b
ON a.Item_ID = b.ItemID
LEFT JOIN Sales c
ON a.Item_Id = c.Item_ID
LEFT JOIN Inventory d
ON a.Item_ID = d.Item_ID

Answer 2

Please try this:
SELECT a.Item_Id, b.product_Name, c.Sales_Qty, d.Remaining_Qty
FROM ProductList a
LEFT JOIN ProductDetail b
ON a.Item_ID = b.Item_ID
LEFT JOIN Sales c
ON a.Item_Id = c.Item_ID
LEFT JOIN Inventory d
ON a.Item_ID = d.Item_ID
This will produce this output:
Item_Id product_Name Sales_Qty Remaining_Qty
---------------------------------------------------
0001 Eraser 15 100
0002 Pencil 20 95
0003 Pen NULL 55
0004 Mouse 50 NULL
If you don't want nulls to be returned, then use COALESCE (if your database is sql server, you can use ISNULL instead of COALESCE) as shown below:
SELECT a.Item_Id, b.product_Name, COALESCE(c.Sales_Qty, 0), COALESCE(d.Remaining_Qty, 0)
FROM ProductList a
LEFT JOIN ProductDetail b
ON a.Item_ID = b.Item_ID
LEFT JOIN Sales c
ON a.Item_Id = c.Item_ID
LEFT JOIN Inventory d
ON a.Item_ID = d.Item_ID
This will produce this output:
Item_Id Item_Name Sales_Qty Remaining_Qty
--------------------------------------------------
0001 Eraser 15 100
0002 Pencil 20 95
0003 Pen 0 55
0004 Mouse 50 0