You work for a famous electronics company that is starting an online store for devices. You are using a dedicated SQL pool. Your team members have a statement that will create a hash distributed table as follows. 
<pre>CREATE TABLE [dbo].[OnlineSales]
( [ProductID]intNOT NULL
, [DateKey]intNOT NULL
, [CustomerID] intNOT NULL
, [DiscountCode]intNOT NULL
, [SalesOrderNumber]nvarchar(20) NOT NULL
, [QuantityNumber] smallint NOT NULL
, [UnitPrice] moneyNOT NULL
, [TotalAmount] moneyNOT NULL
)
WITH
( CLUSTERED COLUMNSTORE INDEX
,DISTRIBUTION = HASH([XXXXX])
)
;</pre>
Which of the following will be the most suitable distribution column?

Answer options:

A.DateKey
B.DiscountCode
C.ProductID
D.QuantityNumber

Correct Answer: C
While selecting a distribution key, there are certain points which we should look into. 
->The column should have many unique values 
->The column should not have null values 
->Shouldn’t be date 
This will help improve parallel processing. ProductID will be the best choice here.
Option A correct: It is a date value.
Option B is incorrect: It may not have much unique values.
Option C is incorrect: This will be the best choice by considering the points listed above.
Option D is incorrect: It may not have much unique values.
Reference: 
To know more about Distribution column selection, please refer to the doc below: 

https://docs.microsoft.com/en-us/azure/synapse-analytics/sql-data-warehouse/sql-data-warehouse-tables-distribute#choose-a-distribution-column-with-data-that-distributes-evenly