Question

We have a sql script to update a set of sequences after seed data populated our tables. The code below would not work:

declare
cursor c1 is 
    select
      'select nvl(max(id),0) from '||uc.table_name sql_text,
      uc.table_name||'_SEQ' sequence_name 
    from
      user_constraints uc,
      user_cons_columns ucc
    where uc.constraint_type='P'
      and ucc.constraint_name = uc.constraint_name
      and ucc.column_name='ID'
      and uc.owner='ME';

alter_sequence_text varchar2(1024);
TYPE generic_cursor_type IS REF CURSOR;
max_id number;
c2 generic_cursor_type;
begin
for r1 in c1 loop
    open c2 for r1.sql_text;
    fetch c2 into max_id;
    close c2;

    if( max_id != 0 ) then
        dbms_output.put_line( 'seq name = '||r1.sequence_name );
        execute immediate 'alter sequence '||r1.sequence_name||' increment by '||to_char(max_id);
        dbms_output.put_line( 'max_id = '||to_char(max_id) );
        execute immediate 'select '||r1.sequence_name||'.nextval from dual';
        dbms_output.put_line( 'sequence value = '||to_char(next_id) );
        execute immediate 'alter sequence '||r1.sequence_name||' increment by 1';
        dbms_output.put_line( 'sequence: '||r1.sequence_name||' is at '||to_char(max_id+1) );
    end if;
end loop;
end;

After searching I found a reference that stated I needed to change the line:

execute immediate 'select '||r1.sequence_name||'.nextval from dual'

and add ‘into next_id;’ (of course declaring next_id appropriately) so the result would be:

execute immediate 'select '||r1.sequence_name||'.nextval from dual into next_id;

I’ve only dealt lightly with pl/sql and sql in general and am interested to know why this change was necessary to make the script work correctly.

Thanks.

Answer 1

When you are using select inside PL/SQL block you have to place data returned by that select statement somewhere. So you have to declare a variable of appropriate data type and use select into clause to put data select returns into that variable even if select statement is executed by execute immediate statement.

Examples

declare
  x number;
begin
  select count(*)
    into x
    from all_objects;
end;


declare
  x number;
begin
  execute immediate 'select count(*)from all_objects' into x;
end;

So your execute immediate statement would be

execute immediate 'select '||sequence_name||'.nextval from dual' into newseqval;

If you are using Oracle 11g onward you can assign sequence’s value directly to a variable, there is no need of using select into clause.

 declare
   x number;
 begin
   x := Sequence_Name.nextval;
 end;