Re: Dynamic table with variable number of columns - Mailing list pgsql-general

Thomas

Bruno Wolff III wrote:

On Tue, Jul 11, 2006 at 06:05:18 -0700,

  nkunkov@optonline.net wrote:

Hello,

I'm a pgsql novice and here is what I'm trying to do:

1.    I need to create a dynamic table with the column names fetched

from the database using a select statement from some other table.  Is

it possible?  Could you point me to a simple example on how to do it?

2.   I would like to compare the list of coulmn names which are values

fetched from some table with the column names of the existing table.

If one of the names doesn't exist as a column name of my table, I'd

like to dynamically alter the table and add a coulmn with the name just

fetched from the DB.

Your help is greatly appreciated.

Thanks

NK

Information on the column names of tables in the database are available

from the information schema and the catlog tables. You can find more about this

in the documentation:

http://www.postgresql.org/docs/8.1/static/information-schema.html

http://www.postgresql.org/docs/8.1/static/catalogs.html

You might get better help by describing the actual problem you are trying to

solve rather than asking for help with a particular approach to solving that

problem. The approach you are trying seems to be seriously broken and it

would probably be a good idea to consider other approaches.

---------------------------(end of broadcast)---------------------------

TIP 1: if posting/reading through Usenet, please send an appropriate

       subscribe-nomail command to majordomo@postgresql.org so that your

       message can get through to the mailing list cleanly

Thank you for the suggestions.

I will try to describe the problem better.

I have two problems to solve.  First one is that I have to transpose a

table.

I have table A that looks like this:

date          product  price description

1/1/2006   prod1      1.00  some product

1/1/2006   prod2      3.00  other product

I need to transpose this table to create table B

date         prod1    prod2

1/1/2006   1.00      3.00

I think I can use EXECUTE statement and build the table dynamically by

using the result of the select statement for column names. Would that

be the right approach?  Are there good examples somewhere on how to

implement this?

My second problem, is that after creating the above transposed table, I

will be inserting more rows to it from table A and i might have more

products too.  That means I will have to compare the value of product

from table A with the column names of table B and alter the table

accordingly.  To compare coulmn names with the value of product in

table A I think I can use pg_attribute function.  Would that be a right

way to go?

Thanks for your help.

NK

---------------------------(end of broadcast)---------------------------

TIP 6: explain analyze is your friend