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How to use Oracle Sequences

December 8, 1997

This section does not discuss the purpose of sequences as such. If you don't know what it's for, read some Oracle documentation.

In many cases it's not necessary to bother with sequences in the client progam. Many programmers prefer to use insert triggers on the tables themselves, and thus not have to worry about primary key constraints. But there are certainly cases where it's much more practical to pass the sequence number back to the client program: If you're inserting rows in several tables with foreign key references you could get the primary keys from sequences to use in the rows that need these references. But again: We're moving into the area of religion now, so reason does not always apply:)

The way to get a sequence value is straightforward:


   select myseq.nextval from dual

In my programs I usually keep a few dummy queries, so the code looks something like:



...
  with DataModule1.Dummy do begin
    sql.clear;
    sql.add('select myseq.nextval from dual');
    open;
    PrimaryKey:=Fields[0].asInteger;
    close;
  end;

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