diff --git a/INSTALL b/INSTALL
index e8cb52c14c..0b5f2eb6ee 100644
--- a/INSTALL
+++ b/INSTALL
@@ -5,6 +5,7 @@ Prerequisites
 -------------
 
  * Python 2.6 or later (http://www.python.org/)
+ * python-sql (http://code.google.com/p/python-sql/)
  * trytond (http://www.tryton.org/)
  * trytond_company (http://www.tryton.org/)
  * trytond_company_work_time (http://www.tryton.org/)
diff --git a/line.py b/line.py
index 541b01689a..9ef785dc99 100644
--- a/line.py
+++ b/line.py
@@ -1,8 +1,12 @@
 #This file is part of Tryton.  The COPYRIGHT file at the top level of
 #this repository contains the full copyright notices and license terms.
+from sql import Literal
+from sql.aggregate import Max, Sum
+from sql.conditionals import Coalesce
+from sql.functions import Extract
+
 from trytond.model import ModelView, ModelSQL, fields
 from trytond.wizard import Wizard, StateView, StateAction, Button
-from trytond.backend import FIELDS
 from trytond.pyson import Eval, PYSONEncoder, Date, Get
 from trytond.transaction import Transaction
 from trytond.pool import Pool
@@ -126,25 +130,24 @@ class HoursEmployee(ModelSQL, ModelView):
 
     @staticmethod
     def table_query():
-        clause = ' '
-        args = [True]
+        pool = Pool()
+        Line = pool.get('timesheet.line')
+        line = Line.__table__()
+        where = Literal(True)
         if Transaction().context.get('start_date'):
-            clause += 'AND date >= %s '
-            args.append(Transaction().context['start_date'])
+            where &= line.date >= Transaction().context['start_date']
         if Transaction().context.get('end_date'):
-            clause += 'AND date <= %s '
-            args.append(Transaction().context['end_date'])
-        return ('SELECT DISTINCT(employee) AS id, '
-                'MAX(create_uid) AS create_uid, '
-                'MAX(create_date) AS create_date, '
-                'MAX(write_uid) AS write_uid, '
-                'MAX(write_date) AS write_date, '
-                'employee, '
-                'SUM(COALESCE(hours, 0)) AS hours '
-            'FROM timesheet_line '
-            'WHERE %s '
-            + clause +
-            'GROUP BY employee', args)
+            where &= line.date <= Transaction().context['end_date']
+        return line.select(
+            line.employee.as_('id'),
+            Max(line.create_uid).as_('create_uid'),
+            Max(line.create_date).as_('create_date'),
+            Max(line.write_uid).as_('write_uid'),
+            Max(line.write_date).as_('write_date'),
+            line.employee,
+            Sum(Coalesce(line.hours, 0)).as_('hours'),
+            where=where,
+            group_by=line.employee)
 
 
 class OpenHoursEmployeeStart(ModelView):
@@ -192,23 +195,25 @@ class HoursEmployeeWeekly(ModelSQL, ModelView):
 
     @classmethod
     def table_query(cls):
-        type_name = FIELDS[cls.year._type].sql_type(cls.year)[0]
-        return ('SELECT id, create_uid, create_date, write_uid, write_date, '
-                'CAST(year AS ' + type_name + ') AS year, week, '
-                'employee, hours '
-            'FROM ('
-                'SELECT EXTRACT(WEEK FROM date) + '
-                    'EXTRACT(YEAR FROM date) * 100 + '
-                    'employee * 1000000 AS id, '
-                'MAX(create_uid) AS create_uid, '
-                'MAX(create_date) AS create_date, '
-                'MAX(write_uid) AS write_uid, '
-                'MAX(write_date) AS write_date, '
-                'EXTRACT(YEAR FROM date) AS year, '
-                'EXTRACT(WEEK FROM date) AS week, employee, '
-                'SUM(COALESCE(hours, 0)) AS hours '
-            'FROM timesheet_line '
-            'GROUP BY year, week, employee) AS ' + cls._table, [])
+        pool = Pool()
+        Line = pool.get('timesheet.line')
+        line = Line.__table__()
+        type_name = cls.year.sql_type().base
+        year_column = Extract('YEAR', line.date).cast(type_name).as_('year')
+        week_column = Extract('WEEK', line.date).as_('week')
+        return line.select(
+            Max(Extract('WEEK', line.date)
+                + Extract('YEAR', line.date) * 100
+                + line.employee * 1000000).as_('id'),
+            Max(line.create_uid).as_('create_uid'),
+            Max(line.create_date).as_('create_date'),
+            Max(line.write_uid).as_('write_uid'),
+            Max(line.write_date).as_('write_date'),
+            year_column,
+            week_column,
+            line.employee,
+            Sum(Coalesce(line.hours, 0)).as_('hours'),
+            group_by=(year_column, week_column, line.employee))
 
 
 class HoursEmployeeMonthly(ModelSQL, ModelView):
@@ -228,20 +233,22 @@ class HoursEmployeeMonthly(ModelSQL, ModelView):
 
     @classmethod
     def table_query(cls):
-        type_name = FIELDS[cls.year._type].sql_type(cls.year)[0]
-        return ('SELECT id, create_uid, create_date, write_uid, write_date, '
-                'CAST(year AS ' + type_name + ') AS year, month, '
-                'employee, hours '
-            'FROM ('
-                'SELECT EXTRACT(MONTH FROM date) + '
-                    'EXTRACT(YEAR FROM date) * 100 + '
-                    'employee * 1000000 AS id, '
-                'MAX(create_uid) AS create_uid, '
-                'MAX(create_date) AS create_date, '
-                'MAX(write_uid) AS write_uid, '
-                'MAX(write_date) AS write_date, '
-                'EXTRACT(YEAR FROM date) AS year, '
-                'EXTRACT(MONTH FROM date) AS month, employee, '
-                'SUM(COALESCE(hours, 0)) AS hours '
-            'FROM timesheet_line '
-            'GROUP BY year, month, employee) AS ' + cls._table, [])
+        pool = Pool()
+        Line = pool.get('timesheet.line')
+        line = Line.__table__()
+        type_name = cls.year.sql_type().base
+        year_column = Extract('YEAR', line.date).cast(type_name).as_('year')
+        month_column = Extract('MONTH', line.date).as_('month')
+        return line.select(
+            Max(Extract('MONTH', line.date)
+                + Extract('YEAR', line.date) * 100
+                + line.employee * 1000000).as_('id'),
+            Max(line.create_uid).as_('create_uid'),
+            Max(line.create_date).as_('create_date'),
+            Max(line.write_uid).as_('write_uid'),
+            Max(line.write_date).as_('write_date'),
+            year_column,
+            month_column,
+            line.employee,
+            Sum(Coalesce(line.hours, 0)).as_('hours'),
+            group_by=(year_column, month_column, line.employee))
diff --git a/setup.py b/setup.py
index 2f7404667f..21a820d99b 100644
--- a/setup.py
+++ b/setup.py
@@ -21,7 +21,7 @@ major_version, minor_version, _ = info.get('version', '0.0.1').split('.', 2)
 major_version = int(major_version)
 minor_version = int(minor_version)
 
-requires = []
+requires = ['python-sql']
 for dep in info.get('depends', []):
     if not re.match(r'(ir|res|webdav)(\W|$)', dep):
         requires.append('trytond_%s >= %s.%s, < %s.%s' %
diff --git a/work.py b/work.py
index e972f4727a..2f78ecaf52 100644
--- a/work.py
+++ b/work.py
@@ -1,5 +1,8 @@
 #This file is part of Tryton.  The COPYRIGHT file at the top level of
 #this repository contains the full copyright notices and license terms.
+from sql import Literal
+from sql.aggregate import Sum
+
 from trytond.model import ModelView, ModelSQL, fields
 from trytond.wizard import Wizard, StateView, StateAction, Button
 from trytond.pyson import PYSONEncoder, Not, Bool, Eval
@@ -105,27 +108,26 @@ class Work(ModelSQL, ModelView):
         in_max = cursor.IN_MAX
         context = transaction.context
 
+        table_w = cls.__table__()
+        table_c = cls.__table__()
+        line = Line.__table__()
         ids = [w.id for w in works]
         hours = dict.fromkeys(ids, 0)
-        date_cond = ''
-        date_args = []
+        where = Literal(True)
         if context.get('from_date'):
-            date_cond = ' AND date >= %s'
-            date_args.append(context['from_date'])
+            where &= line.date >= context['from_date']
         if context.get('to_date'):
-            date_cond += ' AND date <= %s'
-            date_args.append(context['to_date'])
+            where &= line.date <= context['to_date']
         for i in range(0, len(ids), in_max):
             sub_ids = ids[i:i + in_max]
-            red_sql, red_ids = reduce_ids('w.id', sub_ids)
-            cursor.execute('SELECT w.id, SUM(l.hours) '
-                'FROM "' + cls._table + '" AS w '
-                'JOIN "' + cls._table + '" AS c '
-                    'ON c.left >= w.left AND c.right <= w.right '
-                'LEFT JOIN "' + Line._table + '" AS l '
-                    'ON l.work = c.id '
-                'WHERE ' + red_sql + ' ' + date_cond + ' '
-                'GROUP BY w.id', red_ids + date_args)
+            red_sql = reduce_ids(table_w.id, sub_ids)
+            cursor.execute(*table_w.join(table_c,
+                    condition=(table_c.left >= table_w.left)
+                    & (table_c.right <= table_w.right)
+                    ).join(line, 'LEFT', condition=line.work == table_c.id
+                    ).select(table_w.id, Sum(line.hours),
+                    where=red_sql & where,
+                    group_by=table_w.id))
             hours.update(dict(cursor.fetchall()))
         return hours
 
diff --git a/work.xml b/work.xml
index 51a6a9993d..e3570470cd 100644
--- a/work.xml
+++ b/work.xml
@@ -25,7 +25,7 @@ this repository contains the full copyright notices and license terms. -->
         <record model="ir.action.act_window" id="act_work_tree">
             <field name="name">Works</field>
             <field name="res_model">timesheet.work</field>
-            <field name="domain">[('parent', '=', False)]</field>
+            <field name="domain">[('parent', '=', None)]</field>
         </record>
         <record model="ir.action.act_window.view"
             id="act_work_tree_view1">
@@ -71,7 +71,7 @@ this repository contains the full copyright notices and license terms. -->
         <record model="ir.action.act_window" id="act_work_tree2">
             <field name="name">Works</field>
             <field name="res_model">timesheet.work</field>
-            <field name="domain">[('parent', '=', False)]</field>
+            <field name="domain">[('parent', '=', None)]</field>
         </record>
         <record model="ir.action.act_window.view"
             id="act_work_tree2_view1">
@@ -88,7 +88,7 @@ this repository contains the full copyright notices and license terms. -->
         <record model="ir.action.act_window" id="act_work_form2">
             <field name="name">Hours per Work</field>
             <field name="res_model">timesheet.work</field>
-            <field name="domain">[('parent', '=', Get(Eval('timesheet.act_work_tree2', {}), 'id', False))]</field>
+            <field name="domain">[('parent', '=', Get(Eval('timesheet.act_work_tree2', {}), 'id', None))]</field>
         </record>
         <record model="ir.action.act_window.view"
             id="act_work_form2_view1">