Question

I am using Postgres 9.1 and would like to create a sequence which I can use as primary key and which should look like this:

| entity_id_seq |
-----------------
|         X0001 |
|         X0002 |
           ....
|         X0123 |

and nextval( 'entity_id_seq' ) would return 'X0124'.

Any idea’s how and if this is possible with pure Postgres?

Many thanks!

Answer 1

Something like this should be fine:

Create the sequence:

CREATE SEQUENCE special_seq;

Create a function, or not:

CREATE OR REPLACE FUNCTION
nextval_special()
RETURNS TEXT
LANGUAGE sql
AS
$$
    SELECT 'X'||to_char(nextval('special_seq'), 'FM0000'); 
$$;

Now check if it works:

SELECT nextval_special() FROM generate_series(1,10);

 nextval_special 
-----------------
 X0001
 X0002
 X0003
 X0004
 X0005
 X0006
 X0007
 X0008
 X0009
 X0010
(10 rows)

Now you can create the table using the above function:

CREATE TABLE test (
    id TEXT PRIMARY KEY DEFAULT nextval_special(),
    a int
);

or just without function with the simple query from the function:

CREATE TABLE test (
    id TEXT PRIMARY KEY DEFAULT 'X'||to_char(nextval('special_seq'), 'FM0000'),
    a int
);