how to create a sequence in a stored proc?

On Fri, Apr 27, 2012 at 10:37 AM, J.V. <jvsrvcs@gmail.com> wrote:

I need to create a sequence in a stored procedure.

First I need to select a value from a table and set the sequence start value
to that value.

We have a table that does not have a sequence on it, so I want to select the
max value, increment by one
and then start the sequence there.

We have to do this on three databases, I have figured out how to do this in
Oracle (build a string and the EXECUTE IMMEDIATE <myString>, but have not
figured out how to do this with PostgreSQL.

just about any sql is allowed from within a function, including CREATE
SEQUENCE. functions can even create functions and execute them.

merlin

Right, I understand that fully, and have used SQL inside a stored proc
before, but in this case as I mentioned, I need to first do a select
from a table to get a max value, store that in a variable and then use
that variable in a create sequence sql statement.

so I need to construct a string that contains the create sequence
statement and execute that string, at least this is the way it is done
in Oracle.

I do not know how to use a variable in a create sequence statement in
PostgreSQL.

J.V.

On Fri, Apr 27, 2012 at 11:35 AM, J.V. <jvsrvcs@gmail.com> wrote:

Right, I understand that fully, and have used SQL inside a stored proc
before, but in this case as I mentioned, I need to first do a select from a
table to get a max value, store that in a variable and then use that
variable in a create sequence sql statement.

so I need to construct a string that contains the create sequence statement
and execute that string, at least this is the way it is done in Oracle.

I do not know how to use a variable in a create sequence statement in
PostgreSQL.

oh I see. try this:

postgres=# do
$$
declare
s int default 3;
begin
execute 'create sequence v start ' || s;
end;
$$ language plpgsql;
DO

merlin

On 27/04/2012 17:35, J.V. wrote:

Right, I understand that fully, and have used SQL inside a stored proc
before, but in this case as I mentioned, I need to first do a select
from a table to get a max value, store that in a variable and then use
that variable in a create sequence sql statement.

Something like this, off the top of my head and untested:

create or replace function make_sequence_for_table()
returns void
as
$$
declare
max_value integer;
begin
select max(my_column) into max_value from my_table;

create sequence my_sequence
start (max_value + 1)
owned by my_table.my_column;

alter table my_table
alter column my_column
set default nextval('my_sequence');

return;
end;
$$
language plpgsql;

For extra marks, pass the table name in as a parameter, construct the
SQL as a string and execute it using EXECUTE (the pl/pgsql version, not
the command for executing prepared statements).

Ray.

--
Raymond O'Donnell :: Galway :: Ireland
rod@iol.ie

On Apr 27, 2012, at 9:35 AM, J.V. wrote:

Right, I understand that fully, and have used SQL inside a stored proc before, but in this case as I mentioned, I need to first do a select from a table to get a max value, store that in a variable and then use that variable in a create sequence sql statement.

Another approach would be to create the sequence then set the value - you can do that without needing anything more than SQL:

create sequence foo
select setval('foo', (select max(bar) from baz)

so I need to construct a string that contains the create sequence statement and execute that string, at least this is the way it is done in Oracle.

I do not know how to use a variable in a create sequence statement in PostgreSQL.

It depends on the language you're using. For plpgsql it's covered in more detail in the docs, but you could do something like:

create function make_sequence() returns void as $$
declare
newvalue integer;
begin
select max(bar)+1 from baz into newvalue;
execute 'create sequence foo start ' || newvalue;
end;
$$ language plpgsql;

Cheers,
Steve