How to Alter the Position of a Column in a Postgresql Database Table

How do I alter the position of a column in a PostgreSQL database table?

"Alter column position" in the PostgreSQL Wiki says:

PostgreSQL currently defines column
order based on the attnum column of
the pg_attribute table. The only way
to change column order is either by
recreating the table, or by adding
columns and rotating data until you
reach the desired layout.

That's pretty weak, but in their defense, in standard SQL, there is no solution for repositioning a column either. Database brands that support changing the ordinal position of a column are defining an extension to SQL syntax.

One other idea occurs to me: you can define a VIEW that specifies the order of columns how you like it, without changing the physical position of the column in the base table.

How to change the position of column in postgresql without dumping

All you need is a custom insert statement,

For example,

Your table looks like this,

CREATE TABLE "public"."ada" (
    
    "trandate" date, 
    "locname" text, 
    "totusers" integer, 
    "actusers" integer, 
    "datausage" integer, 
    "issues" integer, 
    "id" serial PRIMARY KEY, 
    "issuessolved" integer
);

and the insert statement can be written as

INSERT INTO "public"."ada" (
    "trandate"
    ,"locname"
    ,"totusers"
    ,"actusers"
    ,"datausage"
    ,"issues"
    ,"issuessolved"
    )
VALUES (
    < trandate
    ,date >
    ,< locname
    ,text >
    ,< totusers
    ,integer >
    ,< actusers
    ,integer >
    ,< datausage
    ,integer >
    ,< issues
    ,integer >
    ,< issuessolved
    ,integer >
    );

How to rearrange the column position in PostgreSQL

You can create a VIEW for this,

see following demo

create table foo (entityid int,formattedfilename text);

insert into foo values (1,'file1');
insert into foo values (2,'file2');

select * from foo

RESULT

entityid formattedfilename 
-------- ----------------- 
1        file1             
2        file2             

Now create a view like below

create or replace view vfoo as 
select formattedfilename,entityid from foo .

select * from vfoo

RESULT

formattedfilename entityid 
----------------- -------- 
file1             1        
file2             2  

---

Still you want to do it with the table itself then refer : https://wiki.postgresql.org/wiki/Alter_column_position

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

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.

How to add a new Column in a table after the 2nd or 3rd column in the Table using postgres?

No, there's no direct way to do that. And there's a reason for it - every query should list all the fields it needs in whatever order (and format etc) it needs them, thus making the order of the columns in one table insignificant.

If you really need to do that I can think of one workaround:

• dump and save the description of the table in question (using pg_dump --schema-only --table=<schema.table> ...)
• add the column you want where you want it in the saved definition
• rename the table in the saved definition so not to clash with the name of the old table when you attempt to create it
• create the new table using this definition
• populate the new table with the data from the old table using 'INSERT INTO <new_table> SELECT field1, field2, <default_for_new_field>, field3,... FROM <old_table>';
• rename the old table
• rename the new table to the original name
• eventually drop the old, renamed table after you make sure everything's alright

How to change the column position of MySQL table without losing column data?

Try this:

ALTER TABLE table_name MODIFY password varchar(20) AFTER id

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