The parts are sorted by part number and variant name
Example
If the database contains the 2 parts each with 2 variants: "PartA"-"V1" and "PartA"-"V2" with ERP-Number "1", "PartB"-"V1" and "PartB"-"V2" with ERP-Number "2" then GetPartVariantsByERPNumber("1") returns "PartA"-"V1" and "PartA"-"V2".