Re: Retrieving result of COUNT(*) with PHP

Pardon the label on the last run, it should be seconds.

On 3/28/07, Gavin M. Roy <gmr@xxxxxxxx> wrote:

For large volumes of data, this will be slower.  PostgreSQL has to do more work on select * FROM table than select count(*) from table...

I wrote a little test script to explain this:

Run 1, with numRows: 60348 rows returned, duration of 0.379431 seconds
Run 1, with count: 60348 count returned, duration of 0.061221 seconds

Run 2, with numRows: 60348 rows returned, duration of 0.323478 seconds
Run 2, with count: 60348 count returned, duration of 0.110275 seconds

Run 3, with numRows: 60348 rows returned, duration of 0.379429 miliseconds
Run 3, with count: 60348 count returned, duration of 0.061281 miliseconds

Source Code:

  // pg_NumRows code
  $start = microtime(true);
  $result = pg_Exec($conn, "SELECT i_poemid FROM poetry;");
  $rows = pg_NumRows($result);
  $end = microtime(true) - $start;

  // Count Code
  $start = microtime(true);
  $result = pg_Exec($conn, "SELECT count(*) FROM poetry;");
  $data = "" 0);
  $send = microtime(true) - $start;

In this scenario, i_poemid is the primary key of a table with 60k rows.

Regards,

Gavin

On 3/28/07, Valentín Orfila < valentinorfila@xxxxxxxxx> wrote:

Where people this the way I do, count (*) could be slower

<?
$sql = "select * from TableName";
$count = pg_query($sql);   
$count = pg_num_rows($count);
?>
<td ><?=$count?></td>

I thing that's enough :)

2007/3/28, Mihail Mihailov <Mihail.Mihailov@xxxxxx >:

Hi,

actually, I don't think you need pg_fetch_all.
I use pg_fetch_row for the purpose. What you get with the SELECT
clause is one row.

E.g. like this:
$res = pg_fetch_row(pg_query("SELECT COUNT(*) AS result_count FROM
etc. WHERE etc.")); //Not a very good style :-), one should check if
the query runs
$count = $res[0];

Another way to calculate number of rows in the result is to use
pg_num_rows function.
$res = pg_query("SELECT COUNT(*) AS result_count FROM etc. WHERE etc.");
$count = pg_num_rows($res);

Enjoy!

Mihail



Quoting Lynna Landstreet <lynna@xxxxxxxxxxxxxx >:

> Hi there,
>
> I'm trying to use a SELECT COUNT(*) to count how many results would be
> retrieved from a particular query (as part of the process of paginating
> search results).
>
> But I'm having trouble figuring out how to retrieve the result of the count
> in PHP. The result on its own is a resource rather than a specific value,
> but when I try to retrieve the result via pg_fetch_result, some kind of
> weird math error happens and I get a huge number that bears no resemblance
> to the number of results the query actually gets when it runs (1,714,608 for
> a query that in actuality produces three results).
>
> I tried using an AS clause (SELECT COUNT(*) AS result_count FROM etc. WHERE
> etc.) to give the result a name, but that didn't help, and when I tried
> using pg_fetch_all on the result to see exactly what it was retrieving, I
> got this:
>
> Array
>     (
>         [0] => Array
>            (
>             [result_count] => 1714608
>           )
>
>     )
>
> Again with the weird number. And yet, if I run the exact same query in the
> SQL window of phpPgAdmin, I get the proper result count (3 in this
> instance).
>
> Does anyone know what's going on here? Can I just not use SELECT COUNT(*)
> with PHP at all?
>
> I originally had the script running the actual query and then counting the
> results, and then running it again with LIMIT and OFFSET to get one page's
> worth of results, but it seemed wasteful to do it that way, so I was trying
> to do it more efficiently... :-/
>
> Thanks,
>
> Lynna
>
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