postgresql - Is it possible to change the natural order of columns in Postgres?

Question

Is it possible to change the natural order of columns in Postgres 8.1?

I know that you shouldn't rely on column order - it's not essential to what I am doing - I only need it to make some auto-generated stuff come out in a way that is more pleasing, so that the field order matches all the way from pgadmin through the back end and out to the front end.

Answer 1

You can actually just straight up change the column order, but I'd hardly recommend it, and you should be very careful if you decide to do it.

eg.

# CREATE TABLE test (a int, b int, c int);
# INSERT INTO test VALUES (1,2,3);
# SELECT * FROM test;
 a | b | c 
---+---+---
 1 | 2 | 3
(1 row)

Now for the tricky bit, you need to connect to your database using the postgres user so you can modify the system tables.

# SELECT relname, relfilenode FROM pg_class WHERE relname='test';
 relname | relfilenode 
---------+-------------
 test_t  |       27666
(1 row)

# SELECT attrelid, attname, attnum FROM pg_attribute WHERE attrelid=27666;
 attrelid | attname  | attnum 
----------+----------+--------
    27666 | tableoid |     -7
    27666 | cmax     |     -6
    27666 | xmax     |     -5
    27666 | cmin     |     -4
    27666 | xmin     |     -3
    27666 | ctid     |     -1
    27666 | b        |      1
    27666 | a        |      2
    27666 | c        |      3
(9 rows)

attnum is a unique column, so you need to use a temporary value when you're modifying the column numbers as such:

# UPDATE pg_attribute SET attnum=4 WHERE attname='a' AND attrelid=27666;
UPDATE 1
# UPDATE pg_attribute SET attnum=1 WHERE attname='b' AND attrelid=27666;
UPDATE 1
# UPDATE pg_attribute SET attnum=2 WHERE attname='a' AND attrelid=27666;
UPDATE 1

# SELECT * FROM test;
 b | a | c 
---+---+---
 1 | 2 | 3
(1 row)

Again, because this is playing around with database system tables, use extreme caution if you feel you really need to do this.

This is working as of postgres 8.3, with prior versions, your milage may vary.