Postgres option (dashboard time aggregation)

[zhebrak]

[jacopsd]

for postgres: In file stats.py#53:

time_extract_postgres = "to_char(created_at, 'yyyy:mm:dd:hh24:mi')"
if settings.DATABASES['default']['ENGINE'] == 'django.db.backends.postgresql_psycopg2':
    time_extract = time_extract_postgres