Обсуждение: Counting Row

<div class="Section1"><p class="MsoNormal"><font face="Arial" size="2"><span style="font-size:10.0pt;
font-family:Arial">Hi postgre people. Can anybody help to fix performance of my query?</span></font><p
class="MsoNormal"><fontface="Arial" size="2"><span style="font-size:10.0pt; 
font-family:Arial"> </span></font><p class="MsoNormal"><font face="Arial" size="2"><span style="font-size:10.0pt;
font-family:Arial">Let say, I have <b><span style="font-weight:bold">n</span></b> number of queue ticket. (Which I use
SELECT).</span></font><pclass="MsoNormal"><font face="Arial" size="2"><span style="font-size:10.0pt; 
font-family:Arial">Is there faster method to know where is my ticket number in queue?</span></font><p
class="MsoNormal"><fontface="Arial" size="2"><span style="font-size:10.0pt; 
font-family:Arial"> </span></font><p class="MsoNormal"><font face="Arial" size="2"><span style="font-size:10.0pt;
font-family:Arial">I use (while in PHP script ) and  count one by one until my ticket number match with row  field
.</span></font><pclass="MsoNormal"><font face="Arial" size="2"><span style="font-size:10.0pt; 
font-family:Arial"> </span></font><p class="MsoNormal"><font face="Arial" size="2"><span style="font-size:10.0pt;
font-family:Arial">$sql="select * from [MYTABLE] where [CONDITION] order by [FIELDORDER];</span></font><p
class="MsoNormal"><fontface="Arial" size="2"><span style="font-size:10.0pt; 
font-family:Arial">$rs=&$ctclink->Execute($sql);</span></font><p class="MsoNormal"><font face="Arial"
size="2"><spanstyle="font-size:10.0pt; 
font-family:Arial">$ctr=1;</span></font><p class="MsoNormal"><font face="Arial" size="2"><span style="font-size:10.0pt;
font-family:Arial">$pos=0;</span></font><p class="MsoNormal"><font face="Arial" size="2"><span style="font-size:10.0pt;
font-family:Arial">   </span></font><p class="MsoNormal"><font face="Arial" size="2"><span style="font-size:10.0pt;
font-family:Arial">   while (!$rs->EOF) {</span></font><p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size:10.0pt;
font-family:Arial">      if ($rs->fields[0]==$recid) {</span></font><p class="MsoNormal"><font face="Arial"
size="2"><spanstyle="font-size:10.0pt; 
font-family:Arial">        $pos=$ctr;</span></font><p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size:10.0pt;
font-family:Arial">        break;</span></font><p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size:10.0pt;
font-family:Arial">      } else {</span></font><p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size:10.0pt;
font-family:Arial">      $ctr++;</span></font><p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size:10.0pt;
font-family:Arial">      $rs->MoveNext();  }</span></font><p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size:10.0pt;
font-family:Arial">    }</span></font><p class="MsoNormal"><font face="Arial" size="2"><span style="font-size:10.0pt;
font-family:Arial"> </span></font><p class="MsoNormal"><font face="Arial" size="2"><span style="font-size:10.0pt;
font-family:Arial">   print $pos</span></font><p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size:10.0pt;
font-family:Arial"> </span></font><p class="MsoNormal"><font face="Arial" size="2"><span style="font-size:10.0pt;
font-family:Arial"> </span></font><p class="MsoNormal"><font face="Arial" size="2"><span style="font-size:10.0pt;
font-family:Arial">is there any method to do that with simple??</span></font><p class="MsoNormal"><font face="Arial"
size="2"><spanstyle="font-size:10.0pt; 
font-family:Arial"> </span></font><p class="MsoNormal"><b><font face="Broadway BT" size="3"><span style="font-size:
12.0pt;font-family:"Broadway BT";font-weight:bold">Thanks,</span></font></b><p class="MsoNormal"><font face="Times New
Roman"size="3"><span style="font-size: 
12.0pt"> </span></font></div>

I'd suggest :

- first getting the 'order fields' value for the ticket you want :
SELECT field_order FROM mytable WHERE condition AND  
identifier=the_one_you're_looking_for ORDER BY field_order DESC LIMIT 1

- then counting all the tickets up to this order :

SELECT count(*) FROM mytable WHERE condition AND field_order <= (SELECT  
field_order FROM mytable WHERE condition AND  
identifier=the_one_you're_looking_for ORDER BY field_order DESC LIMIT 1)

You could also use a plpgsql function to reimplement your PHP thing, which  
should be faster than doing it in PHP, but probably slower than the  
example above.


# But there is a simpler solution.

How do you model the position of a ticket in the queue ? What is the  
'order field' you mention ? If your table has a SERIAL PRIMARY KEY, it's  
monotonous, so you can use this without further worries.

table tickets_queues (id SERIAL PRIMARY KEY, queue_id, ticket_id,  
UNIQUE( queue_id, ticket_id)  )

to get the position of a ticket (by its ticket_id) in a queue :

SELECT count(*) FROM tickets_queue WHERE queue_id=# AND id <= (SELECT id  FROM tickets_queue WHERE ticket_id=# AND
queue_id=#)