Thread: datatype conversion on postgresql 7.4.1

hi everybody,

i got the following problem:

i have a database running on a postgresqlserver version 7.4.1, in the 
database is a table with 4 columns containing
float-numbers. what i want to do now is,  to convert the type of those 
columns from float to numeric, because
i want to limit the positions after the decimal point to 2.

what works fine in v. 8:

either

alter table fragment alter column  x type numeric(15,2)

or

update fragment set x = round(x,2)

but both wont work with version 7.4.1!

when i look into the documentation it seems to say that in 7.4.1 round() 
can only round to a given number of positions after the decimal point 
when used with a numeric type, but not with floats!

and if i try something like:

alter table fragment alter column  x type numeric(15,2)

i get an syntax error, so this seems to be no feature in 7.4.1 (didnt 
find anything like that in the docs too....)

what can i do to solve this? there must be some way in postgresql 7.4.1, 
if there is no way to do that, i have to
build up the whole database from scratch........there must be a way to 
convert float to numeric values in 7.4.1 ,
but i dont have a single clue...

thx for any help in advance

Timo Roessner wrote:
> and if i try something like:
> 
> alter table fragment alter column  x type numeric(15,2)
> 
> i get an syntax error, so this seems to be no feature in 7.4.1 (didnt 
> find anything like that in the docs too....)
> 
> what can i do to solve this? there must be some way in postgresql 7.4.1, 
> if there is no way to do that, i have to
> build up the whole database from scratch........there must be a way to 
> convert float to numeric values in 7.4.1 ,
> but i dont have a single clue...

There isn't a way to directly convert the type of a column in 7.4.x but 
you can duplicate the effect.

BEGIN;
ALTER TABLE fragment RENAME COLUMN x TO old_x;
ALTER TABLE fragment ADD COLUMN x numeric(10,2);
UPDATE fragment SET x = old_x;
ALTER TABLE fragment DROP COLUMN old_x;
COMMIT;

Make sure you check any functions/application code that might be 
expecting floating-point rather than numeric before you do this.

Oh, and upgrade from 7.4.1 to 7.4.7 as soon as possible.
--  Richard Huxton  Archonet Ltd