To assure high quality of database applications, testing database applications remains the most popularly used approach. In testing database applications, tests consist of both program inputs and database states. Assessing the adequacy of tests allows targeted generation of new tests for improving their adequacy (e.g., fault-detection capabilities). Comparing to code coverage criteria, mutation testing has been a stronger criterion for assessing the adequacy of tests. Mutation testing would produce a set of mutants (each being the software under test systematically seeded with a small fault) and then measure how high percentage of these mutants are killed (i.e., detected) by the tests under assessment. However, existing test-generation approaches for database applications do not provide sufficient support for killing mutants in database applications (in either program code or its embedded or resulted SQL queries). To address such issues, in this paper, we propose an approach called MutaGen that conducts test generation for mutation testing on database applications. In our approach, we first apply an existing approach that correlates various constraints within a database application through constructing synthesized database interactions and transforming the constraints from SQL queries into normal program code. Based on the transformed code, we generate program-code mutants and SQL-query mutants, and then derive and incorporate query-mutant-killing constraints into the transformed code. Then, we generate tests to satisfy query-mutant-killing constraints. Evaluation results show that MutaGen can effectively kill mutants in database applications, and MutaGen outperforms existing test-generation approaches for database applications in terms of strong mutant killing.