  The competition between the singlet superconducting states with $s$- and
d-wave symmetry of the order parameter is studied within a single-band model
with nearest-neighbor attractive interaction. The zero- and finite-temperature
ground state phase diagrams are constructed for different ratios between the
nearest- and next-nearest-neighbor electron transfer integrals. The mixed
$s+id$ pairing state is shown to form in the intermediate region between $s$-
and d-waves. The temperature phase transitions between the pure and the mixed
pairing state are found.
