> dm() %>% dm_examine_constraints()
Message: i No constraints defined.

> dm_nycflights13() %>% dm_examine_constraints()
Message: ! Unsatisfied constraints:

* Table `flights`: foreign key tailnum into table `planes`: 1640 entries (14.6%) of `flights$tailnum` not in `planes$tailnum`: N722MQ (27), N725MQ (20), N520MQ (19), N723MQ (19), N508MQ (16), ...

> dm_nycflights13(cycle = TRUE) %>% dm_examine_constraints()
Message: ! Unsatisfied constraints:

* Table `flights`: foreign key dest into table `airports`: 242 entries (2.2%) of `flights$dest` not in `airports$faa`: SJU (187), BQN (28), STT (15), PSE (12)
* Table `flights`: foreign key tailnum into table `planes`: 1640 entries (14.6%) of `flights$tailnum` not in `planes$tailnum`: N722MQ (27), N725MQ (20), N520MQ (19), N723MQ (19), N508MQ (16), ...

> dm_nycflights13(cycle = TRUE) %>% dm_select_tbl(-flights) %>%
+   dm_examine_constraints()
Message: i All constraints satisfied.

> # n column
> dm_for_filter_w_cycle() %>% dm_examine_constraints()
Message: i All constraints satisfied.

