Thread: increment Rows in an SQL Result Set postgresql
HI, 1. I have a function that given two parameter produces an arbitrary id, and text. However arbitrary the id and text are, they are in certain order. i.e. it is imperative that whatever processing I do, the order is preserved. 2. An odd thing happens when I perform a join on the result set such that the order that I hope to preserved in destroyed. The same result set but different ordering. I gather this is due to the query planner. Enough said. I was hoping to insert a counter in the select query of 1. such that when I perform the join of 2, I can order by the counter. i.e. 1. select id, astext from function1(1,2) 2. select id, astext, table2.name from function1(1,2) as tmp, table2 where tmp.id = table2.id when I perform 1., I get something of sort id | astext 2 | abc 6 | efg 3 | fhg I will like to preserve ordering.... When I perform 2, I get somthing of sort id | astext | table2.name 6 | efg | joe 2 | abc | zyi 3 | fgh | mec Can someone help such that I get something like id | astext | table2.name | increment 6 | efg | joe | 2 2 | abc | zyi | 1 3 | fgh | mec | 3 Thanks!
Hassan, > 1. I have a function that given two parameter produces an arbitrary id, and > text. However arbitrary the id and text are, they are in certain order. i.e. it > is imperative that whatever processing I do, the order is preserved. What type of function is this? Did you write it in C? An SQL procedure? If the function is written in C, you can create a static local variable which you increment every time you call your function,and which you return along with your other two values. As long as your client is connected to the back-end server,you're guaranteed that it's a single process, and it's not multi-threaded, so this is a safe approach. However, notethat if you disconnect and reconnect, your counter will be reset to zero. If your function is written in a different language or is a procedure, you might create a sequence that your function canquery. The trick is that it is the function itself that must return the incremented value, i.e. you must return three, not two,values from your function. That way, you're not relying on any specific features of the planner, so your three valueswill stick together. Craig
Sadly I didnt write this function. It was written in C and packaged in a shared module .so. I access it thru postgresql
asplpgsql function. I cannot edit the function thus.
I tried this
CREATE TEMPORARY SEQUENCE serial START 1;
SELECT nextval('serial'), astext(tmp.the_geom), street FROM shortest_path_as_geometry('bklion', 185, 10953) AS tmp
LEFTJOIN (SELECT * FROM bklion) AS ss ON ss.the_geom = tmp.the_geom;
I know this is inefficient, and I surely dont know the repercussion of using the temporary sequence in a web
application.Do you?
Appreciate any input.
Thanks!
- Hassan Adekoya
----- Original Message ----
From: Craig A. James <cjames@modgraph-usa.com>
To: Hassan Adekoya <hechy_man@yahoo.com>
Cc: pgsql-performance@postgresql.org
Sent: Saturday, July 15, 2006 1:27:20 PM
Subject: Re: [PERFORM] increment Rows in an SQL Result Set postgresql
Hassan,
> 1. I have a function that given two parameter produces an arbitrary id, and
> text. However arbitrary the id and text are, they are in certain order. i.e. it
> is imperative that whatever processing I do, the order is preserved.
What type of function is this? Did you write it in C? An SQL procedure?
If the function is written in C, you can create a static local variable which you increment every time you call your
function,and which you return along with your other two values. As long as your client is connected to the back-end
server,you're guaranteed that it's a single process, and it's not multi-threaded, so this is a safe approach. However,
notethat if you disconnect and reconnect, your counter will be reset to zero.
If your function is written in a different language or is a procedure, you might create a sequence that your function
canquery.
The trick is that it is the function itself that must return the incremented value, i.e. you must return three, not
two,values from your function. That way, you're not relying on any specific features of the planner, so your three
valueswill stick together.
Craig
Hassan Adekoya wrote: > I will like to preserve ordering.... Tables are inherently unordered. If you want a particular order, you need to use the ORDER BY clause. And you will need to have a column to sort by. If you don't have one, the generate_series() function may help. This has nothing to do with performance, I gather, so it might be more appropriate for the pgsql-sql list. -- Peter Eisentraut http://developer.postgresql.org/~petere/