Обсуждение: Re: Append table

There are two solutions:
You can insert all data from tableB in tableA using a simple insert
select-statement like so:
INSERT INTO tabelA SELECT EmpId, EmpName FROM tabelB;

Or you can visually combine them without actually putting the records in
a single table. That can be with a normal select-union statement or with
a view, something like this:
SELECT EmpId, EmpName FROM tabelA UNION EmpID, EmpName FROM tabelB;

You can use this query as a table-generating subquery in a FROM-clause,
like so:

SELECT * FROM (SELECT EmpId, EmpName FROM tabelA UNION EmpID, EmpName
FROM tabelB) as emps WHERE EmpId = 1;

Or with the view:
CREATE VIEW tabelC AS SELECT EmpId, EmpName FROM tabelA UNION EmpID,
EmpName FROM tabelB;

And then you can use the view as if it was a normal table (altough
inserts are not possible without applying rules to them, see the manual
for that).

SELECT * FROM tabelC WHERE EmpId = 1;

Best regards,

Arjen

On 2-6-2007 17:52 Hanu Kurubar wrote:
> Any luck on appending two table in PostgreSQL.
> Below are two table with same schema that have different values. In this
> case EmpID is unique value.
>
> tabelA
> ------------
> EmpId (Int) EmpName (String)
> 1               Hanu
> 2               Alvaro
>
>
> tabelB
> ------------
> EmpId (Int) EmpName (String)
> 3               Michal
> 4               Tom
>
>
> I would be looking below output after appending tableA with tableB. Is
> this possible in PostgreSQL?
>
>
> tabelA
> ------------
> EmpId (Int) EmpName (String)
> 1               Hanu
> 2               Alvaro
> 3               Michal
> 4               Tom
>
>
>
> Thanks,
> Hanu
>
>
> On 5/30/07, *Hanu Kurubar* <hanu.kurubar@gmail.com
> <mailto:hanu.kurubar@gmail.com>> wrote:
>
>     Can you help me appending two table values into single table without
>     performing INSERT?
>     Note that these tables are of same schema.
>
>     Is there any sql command is supported?
>
>     Thanks,
>     Hanu
>
>
>     On 5/29/07, *Alvaro Herrera* <alvherre@commandprompt.com
>     <mailto:alvherre@commandprompt.com>> wrote:
>
>         Michal Szymanski wrote:
>          > There is another strange thing. We have two versions of our test
>          > >>environment one with production DB copy and second
>         genereated with
>          > >>minimal data set and it is odd that update presented above
>         on copy of
>          > >>production is executing 170ms but on small DB it executing
>         6s !!!!
>          > >
>          > >How are you vacuuming the tables?
>          > >
>          > Using pgAdmin (DB is installed on my laptop) and I use this
>         tool for
>          > vaccuminh, I do not think that vaccuming can help because
>         I've tested on
>          > both database just after importing.
>
>         I think you are misunderstanding the importance of vacuuming the
>         table.
>         Try this: on a different terminal from the one running the test,
>         run a
>         VACUUM on the updated table with vacuum_cost_delay set to 20, on an
>         infinite loop.  Keep this running while you do your update
>         test.  Vary
>         the vacuum_cost_delay and measure the average/min/max UPDATE times.
>         Also try putting a short sleep on the infinite VACUUM loop and
>         see how
>         its length affects the UPDATE times.
>
>         One thing not clear to me is if your table is in a clean
>         state.  Before
>         running this test, do a TRUNCATE and import the data
>         again.  This will
>         get rid of any dead space that may be hurting your measurements.
>
>         --
>         Alvaro
>         Herrera                        http://www.advogato.org/person/alvherre
>         "The Postgresql hackers have what I call a "NASA space shot"
>         mentality.
>         Quite refreshing in a world of "weekend drag racer" developers."
>         (Scott Marlowe)
>
>         ---------------------------(end of
>         broadcast)---------------------------
>         TIP 4: Have you searched our list archives?
>
>                       http://archives.postgresql.org
>         <http://archives.postgresql.org/>
>
>
>
>
>     --
>     With best regards,
>     Hanumanthappa Kurubar
>     Mobile: 98 801 800 65
>
>
>
>
> --
> With best regards,
> Hanumanthappa Kurubar
> Mobile: 98 801 800 65

"Arjen van der Meijden" <acmmailing@tweakers.net> writes:

> There are two solutions:
...
> Or you can visually combine them without actually putting the records in a
> single table. That can be with a normal select-union statement or with a view,
> something like this:
> SELECT EmpId, EmpName FROM tabelA UNION EmpID, EmpName FROM tabelB;

If you're sure the two sets are distinct or you want to get any duplicates and
not eliminate them then if you went with this option you would want to use
"UNION ALL" not just a plain union.

In SQL UNION has to remove duplicates which often involves gathering all the
records and performing a big sort and lots of extra work. UNION ALL is much
faster and can start returning records right away.

--
  Gregory Stark
  EnterpriseDB          http://www.enterprisedb.com

Arjen van der Meijden wrote:
> There are two solutions:
> You can insert all data from tableB in tableA using a simple insert
> select-statement like so:
> INSERT INTO tabelA SELECT EmpId, EmpName FROM tabelB;
>
> Or you can visually combine them without actually putting the records
> in a single table. That can be with a normal select-union statement or
> with a view, something like this:
> SELECT EmpId, EmpName FROM tabelA UNION EmpID, EmpName FROM tabelB;
Since they both have the same schema, you could also combine them by
creating a parent table and making both tables children.  Check out
PostgreSQL's inheritance features.  To make an existing table a child
you'll need to be using PostgreSQL 8.2 or newer.

create table emp_rollup (like tabelA);
alter table tabelA inherits emp_rollup;
alter table tabelB inherits emp_rollup;

Now issue your queries against emp_rollup...  You could also just make
tabelB a child of tabelA:

alter table tabelB inherits tabelA;

But that would mean that if you wanted to query only tabelA you'd have
to modify your query syntax.

select * from ONLY tabelA;

Would only retrieve records from tabelA ...


You could also allow PostgreSQL to limit its index usage based on the
EmpID field by defining some table constraints and enabling constraint
exclusion.
>
> You can use this query as a table-generating subquery in a
> FROM-clause, like so:
>
> SELECT * FROM (SELECT EmpId, EmpName FROM tabelA UNION EmpID, EmpName
> FROM tabelB) as emps WHERE EmpId = 1;
>
> Or with the view:
> CREATE VIEW tabelC AS SELECT EmpId, EmpName FROM tabelA UNION EmpID,
> EmpName FROM tabelB;
>
> And then you can use the view as if it was a normal table (altough
> inserts are not possible without applying rules to them, see the
> manual for that).
>
> SELECT * FROM tabelC WHERE EmpId = 1;
>
> Best regards,
>
> Arjen
>
> On 2-6-2007 17:52 Hanu Kurubar wrote:
>> Any luck on appending two table in PostgreSQL.
>> Below are two table with same schema that have different values. In
>> this case EmpID is unique value.
>>
>> tabelA
>> ------------
>> EmpId (Int) EmpName (String)
>> 1               Hanu
>> 2               Alvaro
>>
>>
>> tabelB
>> ------------
>> EmpId (Int) EmpName (String)
>> 3               Michal
>> 4               Tom
>>
>>
>> I would be looking below output after appending tableA with tableB.
>> Is this possible in PostgreSQL?
>>
>>
>> tabelA
>> ------------
>> EmpId (Int) EmpName (String)
>> 1               Hanu
>> 2               Alvaro
>> 3               Michal
>> 4               Tom
>>


--
Chander Ganesan
The Open Technology Group
One Copley Parkway, Suite 210
Morrisville, NC  27560
Phone: 877-258-8987/919-463-0999
http://www.otg-nc.com
Expert PostgreSQL Training - http://test.otg-nc.com/training-courses/coursedetail.php?courseid=40&cat_id=8