1. Data Source: DB refers to the database where QueryDSL is a query framework that works on top of JDBC or JPA. While DB directly interacts with databases, QueryDSL provides an object-oriented way to construct SQL queries and doesn't connect with databases directly.

2. Type Safety: QueryDSL provides type safety at compile time, ensuring that only valid queries are constructed. On the other hand, DB may not have the same level of type safety, leading to potential errors at runtime if queries are not constructed correctly.

3. API Usage: DB typically requires writing SQL queries manually, which can be error-prone and verbose. In contrast, QueryDSL offers a fluent API that allows for the creation of complex queries in a more concise and readable manner.

4. Join Operations: QueryDSL simplifies the process of creating join queries by providing convenient methods and abstractions for joining tables. This can make complex queries involving multiple tables much easier to construct compared to traditional SQL with DB.

5. Code Generation: QueryDSL offers the capability of generating query classes based on the database schema, which can help in reducing manual effort and ensuring consistency in query construction. DB usually requires writing queries from scratch without such automated code generation features.

In Summary, QueryDSL provides a type-safe, object-oriented approach to construct SQL queries using a fluent API and supports code generation, while DB involves manual SQL query writing directly interacting with databases.