TSQLQuery and fetchrow property?!
lazarus / 16-Databases

----------------------------------------------------------------------
xinyiman · 2019-11-04 14:30

Hi guys, I'll probably ask a stupid question, but I've always used
zeoslib to work with databases. Now I would like to start a new
project using the typical components of lazarus.
In zeoslib the TZQuery object has a propriety named fetchrow that if
set> 0 loads the content of a dbgrid faster. For example, if set to
50, he loads 50 records at a time, he does not wait for the dataset to
be loaded completely to draw the dbgrid. What is the correspondence in
TSQLQuery?

----------------------------------------------------------------------
Zvoni · 2019-11-04 15:08

Not sure there is one.
If you think about it, it's more a function of the SQL-dialect used by
the Database.
What you're describing would be
on MySQL: SELECT SomeColumn FROM SomeTable WHERE Name='SomeName' LIMIT
50
on MSSQL: SELECT TOP 50 SomeColumn FROM SomeTable WHERE
Name='SomeName'
on DB2: SELECT SomeColumn FROM SomeTable WHERE Name='SomeName' FETCH
FIRST 50 ROWS ONLY

The implemenation would be different for different Databases.

----------------------------------------------------------------------
xinyiman · 2019-11-04 15:11

I think I understand, it would seem that the parameter is
PacketRecords. But it seems that you only load the first N records,
then when I browse the dbgrid it loads them all. I don't understand if
you load them N at a time or just need to load the first N records
faster, and then the others do them at once.

----------------------------------------------------------------------
Thaddy · 2019-11-04 15:22

Fetching all or too many records kills your application. That's why.

----------------------------------------------------------------------
Zvoni · 2019-11-04 15:22

Thx, i was looking for that Property too.

As i understood it: it loads N at a time
QuoteFor performance reasons, SqlDB does not read all records when
opening TSQLQuery by default, only the first 10. Only when the
eleventh record is accessed will the next set of 10 records be loaded,
etc.
But:
QuoteAn alternative is available. The number of records returned by
the server is set by the '.PacketRecords' property. The default value
is 10; if you make it -1 then all records will be loaded at once.