[Lazarus] Web development and XML database (Mattias)
graemeg.lists at gmail.com
Wed Nov 16 16:36:31 CET 2011
On 16/11/2011, Juha Manninen <juha.manninen62 at ....> wrote:
> I guess your queries fetch from one table only. Complex SQL queries with
> many joins can be really slow, even with correct indexes.
Nope, we often fetch from many tables. True, single table queries are
just a couple of milliseconds, and multiple table queries are still
far under 1 second. See attached image - status bar values, using the
following query. This is just something I put quickly together as an
example. Not extensive, but an example none the less.
select distinct l.Username, a.City, c.NAME as CountryName,
t.ADDRESSDESCRIPTION from LEARNER l
inner join ADDRESS a on
a.OWNER_OID = l.OID
inner join COUNTRY c on
c.OID = a.COUNTRY_OID
inner join ADDRESSTYPE t on
t.OID = a.ADDRESSTYPE_OID
Our reports use much more extensive queries, but results are still
instant (way under a second).
As an explanation of the values in the status bar of the screenshot.
Record count - this should be obvious ;-)
Time to execute.... - this is how long the sql execution took and
returned a resultset.
Time to download... - this is how long it took to generate Objects
based on the resultset (our apps GUI & CGI use objects everywhere,
One of our screens that our CGI and GUI apps generates is a treeview.
It pulls back just enough information to build the tree. The treeview
contains about +- 70,000-80,000 nodes. Retrieving that data and
building objects from it is also near instant.
But yes, SQL queries can take long too - depending on what it must do.
I have worked on project where we had to do data conversion from a IBM
mainframe system to a Intel based SQL Server 2000 database. A full
data conversion had to be run on Friday's, and normally only ended on
Monday morning (if no failures occurred). That's 2.5-3.0 days
continuous running, resulting in a 8GB SQL Server database. But this
is an extreme case. :)
- Graeme -
fpGUI - a cross-platform Free Pascal GUI toolkit
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