After run the pin_assignments.tcl and perform compilation. You will get warning as below:
Warning (181009): DQ I/O pins fed by DQS I/O pin "I/O pad mem_dqs[*]" assigned different I/O standards -- it is recommended that all DQ I/O pins fed by the same DQS I/O pin have the same I/O standard
This is due to the fact that legality checks don't understand that differential and single-ended I/O standards are actually the same.
This warning can be safely ignored.
This issue will be fixed in a future version of the Quartus® II software.