Question

CREATE FUNCTION dbo.GetCustomers
(
  @ZIPCode VARCHAR(255)
)
RETURNS TABLE

AS BEGIN
SELECT * dbo.GetCustomers
WHERE dbo.GetCustomers.ZIPCODE = ZIPCode 
RETURN
END

Im not familar with the syntax. Please help.

Answer 1

It would have been worth guessing that the parameter @ZIPCode would go into the query as @ZIPCode

CREATE FUNCTION dbo.GetCustomers
(
  @ZIPCode VARCHAR(255)
)
RETURNS TABLE

AS
RETURN (
    SELECT * FROM dbo.Customers
    WHERE dbo.Customers.ZIPCODE = @ZIPCode
    )
END

Your first attempt WHERE dbo.Customers.ZIPCODE = ZIPCode is the same as WHERE dbo.Customers.ZIPCODE = dbo.CustomersZIPCode. That is, return all rows