Difference between Query Expression AND Fetch XML query

Query Expression:- It is the mostly commonly used way for querying information in CRM. Probably because it uses the object-oriented style of coding and so you have distinct classes for query, condition, columns etc. You have intelligence to support you when writing a query using Query Expression. However, it has its own limitations, one of them being the inability to provide a column of a linked entity to be returned as the query result. This perhaps because the Query Expression would return a dynamic entity or a strongly typed base entity and so it is unable to return columns of related entity. Fetch XML Query :- Fetch XML requires the query to be specified in XML format and the result set is returned in XML format as well. This allows Fetch XML to return related entity columns as well as this is just another node in the xml doc.