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Thread: PL/PGSQL - How to pass in variables?

PL/PGSQL - How to pass in variables?

From
"Scott Yohonn"
Date:
Using PL/PGSQL, I am trying to create a procedure to display the
count of rows in any single table of a database. The End-user would
pass in a table name and the prodecure would display the table name
with the row count.
I am able to hardcode the variable for table and get the appropriate
results from my count function (see below), but cannot pass in a
variable and have the function work. Any suggesstions???
 
CREATE FUNCTION get_table_count(tablename text) RETURNS integer AS $$
DECLARE
     
     --tablename ALIAS FOR $1;
     
      rowcount INTEGER;
   BEGIN
     
     SELECT INTO rowcount count(*) FROM tablename;
     
     RETURN rowcount;
     
   END;
 $$ LANGUAGE 'plpgsql';
 

Re: PL/PGSQL - How to pass in variables?

From
Jean-Paul Argudo
Date:
Hi Scott,

You'll have to execute dynamic SQL (see doc chapter "36.6.5. Executing
Dynamic Commands") for your function to work:

CREATE FUNCTION get_table_count(tablename text) RETURNS integer AS
$$
DECLARE   --tablename ALIAS FOR $1;    rowcount INTEGER; BEGIN
   execute 'SELECT count(*) FROM '||tablename into rowcount;   return rowcount;
 END;
$$ LANGUAGE 'plpgsql';


select get_table_count('bar');
get_table_count
-----------------              3
(1 row)




Cheers,

-- 
Jean-Paul Argudo
www.PostgreSQLFr.org
www.dalibo.com

Re: PL/PGSQL - How to pass in variables?

From
"Jaime Casanova"
Date:
On 5/14/06, Scott Yohonn <syohonn@gmail.com> wrote:
>
> Using PL/PGSQL, I am trying to create a procedure to display the
> count of rows in any single table of a database. The End-user would
> pass in a table name and the prodecure would display the table name
> with the row count.
> I am able to hardcode the variable for table and get the appropriate
> results from my count function (see below), but cannot pass in a
> variable and have the function work. Any suggesstions???
>
> CREATE FUNCTION get_table_count(tablename text) RETURNS integer AS $$
> DECLARE
>
>      --tablename ALIAS FOR $1;
>
>       rowcount INTEGER;
>    BEGIN
>
>      SELECT INTO rowcount count(*) FROM tablename;
>
>      RETURN rowcount;
>
>    END;
>  $$ LANGUAGE 'plpgsql';
>

you can't do this because tablename is a variable not a table, you
have to append the content of the variable in a string that can be
EXECUTE'd
    EXECUTE 'SELECT count(*) FROM ' || tablename INTO rowcount;

--
regards,
Jaime Casanova

"Programming today is a race between software engineers striving to
build bigger and better idiot-proof programs and the universe trying
to produce bigger and better idiots.
So far, the universe is winning."                                      Richard Cook

Re: PL/PGSQL - How to pass in variables?

From
Jean-Paul Argudo
Date:
Scott Yohonn wrote:
> Jean-Paul,
> 
> Thanks! This did work. The output put the name of the function
> (get_table_count) as the header. How would I display the name of the table
> that I am requesting the row count of?

The only way I know is to alias the output in the query calling the
function, so:


select get_table_count('bar') as bar;
bar
-----  3
(1 row)

I don't know any other way to do that...

Cheers,

-- 
Jean-Paul Argudo
www.PostgreSQLFr.org
www.dalibo.com