Merlin Moncure wrote:
On 10/13/06, Roman Neuhauser <neuhauser@xxxxxxxxxx> wrote:
SELECT * FROM TABLE ORDER BY pk LIMIT 10 OFFSET N;
using offset to walk a table is extremely poor form because of:
* poor performance
* single user mentality
* flat file mentality
databases are lousy at this becuase they inheritly do not support
abolute addressing of data -- nore should they, beause this is not
what sql is all about. in short, 'offset' is a hack, albeit a useful
one in some cases, but dont gripe when it doesn't deliver the goods.
for server side browsing use cursors or a hybrid pl/pgqsl loop. for
client side, browse fetching relative to the last key:
select * from foo where p > p1 order by p limit k;
This does require some way for the client to keep a single transaction
open. If this kind of query is performed by a web application (as is
often the case), the "client" is the server side web script engine, and
not all of those beasts are capable of keeping a transaction open across
pages (PHP comes to mind).
This combined with expensive (complex) queries is regularly a pain.
The alternative solution of storing the query results in a temporary
table suffers from the same problem (the transaction is gone after the
first page).
I believe, as a result of this, it is not uncommon to pass the primary
key id's of all results on in a hidden field, so they are available for
quick querying on proceeding pages.
--
Alban Hertroys
alban@xxxxxxxxxxxxxxxxx
magproductions b.v.
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