How To Find Matching Records in 2 Tables

Using join

SELECT fos.customerkey FROM Fact_OpenSalesOrdersHeader as FOS inner join dim_customer as cus on fos.customerkey = cus.customerkey

Using Intersect

select customerkey from Fact_OpenSalesOrdersHeader intersect select customerkey from dim_customer

Using In

select distinct customerkey from Fact_OpenSalesOrdersHeader where customerkey in(select customerkey from dim_customer)