Join two tables in SQL Server

Question

I have to tables

Customer

CustomerID   Name        Surname
---------------------------------
  1          Adam        Test
  2          Robert      Test2
  3          John        Test3

CustomerAddress

CustomerAddressId  CustomerId     AddressId
-------------------------------------------
1                  1              1
2                  1              2
3                  1              3
4                  2              6
5                  2              7
6                  2              8

I want to select CustomerId from these two tables.

I wrote this query but it multiplies my records.

What query did you write? It would be helpful for us to have the query, expected output, etc. — Jeffrey Van Laethem
– Jeffrey Van Laethem, Commented Nov 15, 2018 at 15:53
you have 2 proposed answers below check them out and either will get you the non multiplied answers your looking for. @adamek339 — junketsu
– junketsu, Commented Nov 15, 2018 at 18:39

Jeffrey Van Laethem · Accepted Answer · 2018-11-15 15:52:24Z

2

If you're looking for a distinct list of CustomerId from both tables, it'll be easiest to use UNION:

SELECT CustomerId
FROM Customer
UNION SELECT CustomerId
FROM CustomerAddress

Using UNION ALL would show duplicates in your result set.

answered Nov 15, 2018 at 15:52

Jeffrey Van Laethem

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Yogesh Sharma · Accepted Answer · 2018-11-15 15:41:11Z

1

You can use DISTINCT keyword with JOIN :

SELECT DISTINCT C.CustomerId     
FROM Customer c INNER JOIIN
     CustomerAddress cs
     ON CD.CustomerId = C.CustomerId;

Without DISTINCT it would return multiple CustomerIds as because of second table has multiple address for same customer.

answered Nov 15, 2018 at 15:41

Yogesh Sharma

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Comments

Zeki Gumus · Accepted Answer · 2018-11-15 15:50:28Z

1

If you want to capture Customers which has addresses you can use following script :

SELECT * 
FROM Customer C
WHERE EXISTS (SELECT 1 FROM CustomerAddress CA WHERE C.CustomerId=CA.CustomerId)

answered Nov 15, 2018 at 15:50

Zeki Gumus

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