select
  a.*
  , table_name = 'Table1'
from Table1 a
union all
select
  b.*
  , table_name = 'Table2'
from Table2 b
...
union all
select
  z.*
  , table_name = 'Table26'
from Table26 z

select
  id, name, description, value , cast(field_z as nvarchar) + (cast field_y as nvarchar) as common_field
  , table_name = 'Table1'
from Table1 a
union all
select
 id, name, description, value , cast(field_x as nvarchar) + (cast field_t as nvarchar) as common_field
  , table_name = 'Table2'
from Table2 b
...

select
  id, name, description, value , field_z, field_y , null as field_x, null as field_t
  , table_name = 'Table1'
from Table1 a
union all
select
  id, name, description, value , null as field_z, null as field_y ,   field_x,   field_t
  , table_name = 'Table2'
from Table2 b
...

SELECT A.*,
       B.*
FROM A 
        INNER JOIN temp_tab ON A.OPERATION_ID = temp_tab.OPERATION_ID AND 
                                  A.sys_code = temp_tab.sys_code AND 
                                  A.message_id = temp_tab.message_id
        OUTER JOIN B ON temp_tab.OPERATION_ID = B.OPERATION_ID AND 
                                   temp_tab.sys_code = B.sys_code AND 
                                   temp_tab.message_id = B.message_id

LEFT OUTER JOIN

LEFT OUTER JOIN

LEFT JOIN

select A.*,B.*,C.*,D.*,E.*
from A,B,C,D,E
where A.id=B.id and A.id=C.id and A.id=D.id and  A.id=E.id and
A.name=B.name and A.name=C.name and A.name=D.name and  A.id=E.name and
A.description=B.description and A.description=C.description and A.description=D.description and  A.description=E.description and
A.value=B.value and A.value=C.value and A.value=D.value and  A.value=E.value