GL Other - Calendar Validation

SELECT 
       m1.period_set_name period_set_dg,
       m1.period_type period_type_dg,
       m2.period_name before_per_dg,
       m3.period_name after_per_dg, 
       m1.accounting_date gap_start_date_dg,
       m3.accounting_date-1 gap_end_date_dg
FROM   gl_date_period_map m1,
       gl_date_period_map m2,
       gl_date_period_map m3
WHERE
      m1.accounting_date between :date_low 
                                                  and :date_high
AND   m1.period_name = 'NOT ASSIGNED'
AND   m2.period_set_name = :periodset
AND   m2.period_type = :periodtype
AND   m2.accounting_date+0 between :date_low 
                                                    and :date_high
AND   m2.accounting_date = m1.accounting_date-1
AND   m2.period_name != 'NOT ASSIGNED'
AND   m3.period_set_name = :periodset
AND   m3.period_type = :periodtype
AND   m3.accounting_date =
       ( SELECT min(m4.accounting_date)
         FROM gl_date_period_map m4 
         WHERE m4.period_set_name = :periodset
         AND   m4.period_type = :periodtype
         AND   m4.accounting_date between 
                  m1.accounting_date and :date_high
         AND   m4.period_name != 'NOT ASSIGNED' ) 
 and m1.period_set_name=:periodset 
 and m1.period_type=:periodtype
ORDER BY m1.accounting_date