Re: Query performance problem

See the syntax for INSERT ... SELECT shown here:
http://www.postgresql.org/docs/8.0/static/sql-insert.html

Instead of doing a nested loop to INSERT new records, do it like this:

For ($period = start; $period < end; $period++)
{
INSERT INTO chartdetails (accountcode, period)
SELECT accountcode, $period FROM chartdetails WHERE
(accountcode, $period) NOT IN (
SELECT accountcode, period FROM chardetails WHERE period =
$period
);
}

Or if you have some table that has 1 row for each period (call it
"periods") then you could simply do:

INSERT INTO chartdetails (accountcode, period)
SELECT accountcode, period FROM accountcode, period
WHERE (period BETWEEN $start AND $end) AND (accountcode,
period) NOT IN (
SELECT accountcode, period FROM chartdetails WHERE period
BETWEEN $start AND $end
);

Note to others: see the legitimate use of an unconstrained CROSS JOIN?

----------------------------------------------------------------------

Postgres's SELECT count(*) is slow if many records meet the WHERE clause
being used. It looks like you're only using testing for 0 or >0 in your
query, so you could use:

SELECT EXISTS (SELECT 1 FROM chartdetails WHERE <where clause goes here>);

This will be much faster since with EXISTS, postgres only runs the query
long enough to find out whether even one row would be returned--if so,
it stops.

Regards,
Paul Tillotson

Phil Daintree wrote:

>Dear psqlers,
>
>I need your help!
>
>I administer/develop an open source PHP accounting software project (webERP) [snip....]
>
>
> $ChartAccounts = DB_query('SELECT accountcode FROM chartmaster',$db);
>
> While ($AccountRow = DB_fetch_array($ChartAccounts)){
>
> for ($PeriodNo=$CreateFrom;$PeriodNo <= $CreateTo;$PeriodNo++) {
>
> echo '<LI>' . _('Period Number') . ' ' . $PeriodNo . '</LI>';
>
> // Check if there is an chart details record set up
> $sql = 'SELECT count(*) FROM chartdetails
> WHERE accountcode='.$AccountRow['accountcode'].'
> AND period=' . $PeriodNo;
> $InsChartDetails = DB_query($sql,$db,'','','',false);
> $CountRows = DB_fetch_row($InsChartDetails);
> $AccountExistsAlready = $CountRows[0];
> DB_free_result($InsChartDetails);
> if(! $AccountExistsAlready) {
> $sql = 'INSERT INTO chartdetails (accountcode,
> period)
> VALUES (' . $AccountRow['accountcode'] . ',
> ' . $PeriodNo . ')';
> $InsChartDetails = DB_query($sql,$db);
> DB_free_result($InsChartDetails);
> }
>
> }
>
> /*Now run through each of the new chartdetail records created for each
>account and update them with the B/Fwd and B/Fwd budget no updates would be
>required where there were previously no chart details set up ie
>FirstPeriodPostedTo > 0 */
>
> for ($PeriodNo=$CreateFrom;$PeriodNo<=$CreateTo; $PeriodNo++) {
>
> $sql = 'SELECT accountcode,
> period,
> actual + bfwd AS cfwd,
> budget + bfwdbudget AS cfwdbudget
> FROM chartdetails WHERE period =' . ($PeriodNo - 1);
> $ChartDetailsCFwd = DB_query($sql,$db);
>
> while ($myrow = DB_fetch_array($ChartDetailsCFwd)){
>
> $sql = 'UPDATE chartdetails SET bfwd =' . $myrow['cfwd'] . ',
> bfwdbudget =' . $myrow['cfwdbudget'] . '
> WHERE accountcode = ' . $myrow['accountcode'] . '
> AND period >=' . $PeriodNo;
> $UpdChartDetails = DB_query($sql,$db, '', '', '', false);
> DB_free_result($UpdChartDetails);
> }
> DB_free_result($ChartDetailsCFwd);
> }
>
> }
>
>
>