Calcular horas de trabalho entre 2 datas no PostgreSQL

Resultados arredondados

Para apenas dois carimbos de data/hora fornecidos

SELECT count(*) AS work_hours
FROM   generate_series (timestamp '2013-06-24 13:30'
                      , timestamp '2013-06-24 15:29' - interval '1h'
                      , interval '1h') h
WHERE  EXTRACT(ISODOW FROM h) < 6
AND    h::time >= '08:00'
AND    h::time <= '14:00';

• 
  A função generate_series() gera uma linha se o final for maior que o início e outra linha para cada cheio determinado intervalo (1 hora). Esta contagem cada hora entrada . Para ignorar horas fracionárias, subtraia 1 hora do final. E não conte horas começando antes das 14:00.
  
• 
  Use o padrão de campo ISODOW em vez de DOW para EXTRACT() para simplificar expressões. Retorna 7 em vez de 0 para domingos.
  
• 
  Uma conversão simples (e muito barata) para time facilita a identificação das horas qualificadas.
  
• 
  As frações de uma hora são ignoradas, mesmo se as frações no início e no final do intervalo somarem uma hora ou mais.
  

Para uma mesa inteira

CREATE TEMP TABLE t (t_id int PRIMARY KEY, t_start timestamp, t_end timestamp);
INSERT INTO t VALUES 
  (1, '2009-12-03 14:00', '2009-12-04 09:00')
 ,(2, '2009-12-03 15:00', '2009-12-07 08:00')  -- examples in question
 ,(3, '2013-06-24 07:00', '2013-06-24 12:00')
 ,(4, '2013-06-24 12:00', '2013-06-24 23:00')
 ,(5, '2013-06-23 13:00', '2013-06-25 11:00')
 ,(6, '2013-06-23 14:01', '2013-06-24 08:59');  -- max. fractions at begin and end

SELECT t_id, count(*) AS work_hours
FROM  (
   SELECT t_id, generate_series (t_start, t_end - interval '1h', interval '1h') AS h
   FROM   t
   ) sub
WHERE  EXTRACT(ISODOW FROM h) < 6
AND    h::time >= '08:00'
AND    h::time <= '14:00'
GROUP  BY 1
ORDER  BY 1;

Mais precisão

SELECT t_id, count(*) * interval '5 min' AS work_interval
FROM  (
   SELECT t_id, generate_series (t_start, t_end - interval '5 min', interval '5 min') AS h
   FROM   t
   ) sub
WHERE  EXTRACT(ISODOW FROM h) < 6
AND    h::time >= '08:00'
AND    h::time <= '14:55'  -- 15.00 - interval '5 min'
GROUP  BY 1
ORDER  BY 1;

Limpador com LATERAL no Postgres 9.3+

SELECT t.t_id, h.work_hours
FROM   t
LEFT   JOIN LATERAL (
   SELECT count(*) AS work_hours
   FROM   generate_series (t.t_start, t.t_end - interval '1h', interval '1h') h
   WHERE  EXTRACT(ISODOW FROM h) < 6
   AND    h::time >= '08:00'
   AND    h::time <= '14:00'
   ) h ON TRUE
ORDER  BY 1;

SELECT t.t_id, h.work_interval
FROM   t
LEFT   JOIN LATERAL (
   SELECT count(*) * interval '5 min' AS work_interval
   FROM   generate_series (t.t_start, t.t_end - interval '5 min', interval '5 min') h
   WHERE  EXTRACT(ISODOW FROM h) < 6
   AND    h::time >= '08:00'
   AND    h::time <= '14:55'
   ) h ON TRUE
ORDER  BY 1;

• Encontre os elementos mais comuns em uma matriz com um grupo por
• Inserir várias linhas em uma tabela com base no número em outra tabela

Resultados exatos

Postgres 8.4+

WITH var AS (SELECT '08:00'::time  AS v_start
                  , '15:00'::time  AS v_end)
SELECT t_id
     , COALESCE(h.h, '0')  -- add / subtract fractions
       - CASE WHEN EXTRACT(ISODOW FROM t_start) < 6
               AND t_start::time > v_start
               AND t_start::time < v_end
         THEN t_start - date_trunc('hour', t_start)
         ELSE '0'::interval END
       + CASE WHEN EXTRACT(ISODOW FROM t_end) < 6
               AND t_end::time > v_start
               AND t_end::time < v_end
         THEN t_end - date_trunc('hour', t_end)
         ELSE '0'::interval END                 AS work_interval
FROM   t CROSS JOIN var
LEFT   JOIN (  -- count full hours, similar to above solutions
   SELECT t_id, count(*)::int * interval '1h' AS h
   FROM  (
      SELECT t_id, v_start, v_end
           , generate_series (date_trunc('hour', t_start)
                            , date_trunc('hour', t_end) - interval '1h'
                            , interval '1h') AS h
      FROM   t, var
      ) sub
   WHERE  EXTRACT(ISODOW FROM h) < 6
   AND    h::time >= v_start
   AND    h::time <= v_end - interval '1h'
   GROUP  BY 1
   ) h USING (t_id)
ORDER  BY 1;

Postgres 9.2+ com tsrange

CREATE OR REPLACE FUNCTION f_worktime_1day(_start timestamp, _end timestamp)
  RETURNS interval AS
$func$  -- _start & _end within one calendar day! - you may want to check ...
SELECT CASE WHEN extract(ISODOW from _start) < 6 THEN (
   SELECT COALESCE(upper(h) - lower(h), '0')
   FROM  (
      SELECT tsrange '[2000-1-1 08:00, 2000-1-1 15:00)' -- hours hard coded
           * tsrange( '2000-1-1'::date + _start::time
                    , '2000-1-1'::date + _end::time ) AS h
      ) sub
   ) ELSE '0' END
$func$  LANGUAGE sql IMMUTABLE;

CREATE OR REPLACE FUNCTION f_worktime(_start timestamp
                                    , _end timestamp
                                    , OUT work_time interval) AS
$func$
BEGIN
   CASE _end::date - _start::date  -- spanning how many days?
   WHEN 0 THEN                     -- all in one calendar day
      work_time := f_worktime_1day(_start, _end);
   WHEN 1 THEN                     -- wrap around midnight once
      work_time := f_worktime_1day(_start, NULL)
                +  f_worktime_1day(_end::date, _end);
   ELSE                            -- multiple days
      work_time := f_worktime_1day(_start, NULL)
                +  f_worktime_1day(_end::date, _end)
                + (SELECT count(*) * interval '7:00'  -- workday hard coded!
                   FROM   generate_series(_start::date + 1
                                        , _end::date   - 1, '1 day') AS t
                   WHERE  extract(ISODOW from t) < 6);
   END CASE;
END
$func$  LANGUAGE plpgsql IMMUTABLE;

SELECT t_id, f_worktime(t_start, t_end) AS worktime
FROM   t
ORDER  BY 1;