Find missing values in a sequence with SQL

missing_values_sequence.sql

SELECT start, stop FROM (
  SELECT m.<number_field> + 1 AS start,
    (SELECT min(<number_field>) - 1 FROM <table> AS x WHERE x.<number_field> > m.<number_field>) AS stop
  FROM <table> AS m
    LEFT OUTER JOIN <table> AS r ON m.<number_field> = r.<number_field> - 1
  WHERE r.<number_field> IS NULL
) AS x
WHERE stop IS NOT NULL 
ORDER BY start;