How I can delete all records from data set
lazarus / 16-Databases

----------------------------------------------------------------------
ribarvlada · 2011-08-18 19:29

I use Zeoslib 7 . I need to delete all records from my table.
Can I use something like Clipper's command ZAP or  function DBZAP().
I was found DataSet.EmptyDataSet, but nothin was deleted.
Then I try :

 ZQueryRacun.Open;
  ZQueryRacun.First;
  while not ZQueryRacun.EOF do begin
    ZQueryRacun.Delete;
  end;

but I'm afraid that it is very slow for large database.

----------------------------------------------------------------------
eny · 2011-08-18 19:43

Can't you execute SQL?
Something like: DELETE FROM <tablename>?

----------------------------------------------------------------------
Arbee · 2011-08-18 19:54

What kind of database do you have?  Some SQL "dialects" have something
like a TRUNCATE TABLE, which is especially devoted to deleting
everything in a table very fast.

----------------------------------------------------------------------
eny · 2011-08-18 20:17

Quote from: Arbee on August 18, 2011, 09:54:24 pmWhat kind of database
do you have?  Some SQL "dialects" have something like a TRUNCATE
TABLE, which is especially devoted to deleting everything in a table
very fast.
TRUNCATE TABLE is not really SQL; Oracle for example supports this but
you need special permissions for it.

----------------------------------------------------------------------
joseme · 2011-08-18 20:47

ZQueryRacun.Close;
ZQueryRacun.SQL.Text:='delete from mytable';
ZQueryRacun.ExecQuery;

----------------------------------------------------------------------
ribarvlada · 2011-08-18 20:55

Thanks all of you!

----------------------------------------------------------------------
SteveF · 2011-08-19 15:59

If you're migrating from an Xbase-type DBMS (dBase, FoxPro et al) to a
SQL DBMS (MySQL, PostgreSQL, Firebird, etc) I highly recommend finding
a good basic book on SQL. 

Many things which require the step-like iteration through the records
in an Xbase system can be done much more efficiently in SQL--if one
knows how.  The book will supply that information.

Steve