Padding a string in Postgresql with rpad without truncating it - sql

Question

Using Postgresql 8.4, how can I right-pad a string with blanks without truncating it when it's too long?
The problem is that rpad truncates the string when it is actually longer than number of characters to pad. Example:
SELECT rpad('foo', 5); ==> 'foo ' -- fine
SELECT rpad('foo', 2); ==> 'fo' -- not good, I want 'foo' instead.
The shortest solution I found doesn't involve rpad at all:
SELECT 'foo' || repeat(' ', 5-length('foo')); ==> 'foo ' -- fine
SELECT 'foo' || repeat(' ', 2-length('foo')); ==> 'foo' -- fine, too
but this looks ugly IMHO. Note that I don't actually select the string 'foo' of course, instead I select from a column:
SELECT colname || repeat(' ', 30-length(colname)) FROM mytable WHERE ...
Is there a more elegant solution?

Answer 1

found a slightly more elegant solution:
SELECT greatest(colname,rpad(colname, 2));
eg:
SELECT greatest('foo',rpad('foo', 5)); -- 'foo '
SELECT greatest('foo',rpad('foo', 2)); -- 'foo'
.
To explain how it works:
rpad('foo',5) = 'foo ' which is > 'foo' (greatest works with strings as well as numbers)
rpad('foo',2) = 'fo' which is < 'foo', so 'foo' is selected by greatest function.
if you want left-padded words you cant use greatest because it compares left-to-right (eg 'oo' with 'foo') and in some cases this will be greater or smaller depending on the string. I suppose you could reverse the string and use the rpad and reverse it back, or just use the original solution which works in both cases.

Answer 2

If you don't want to write that repeat business all the time, just write your own function for it. Something like this:
create or replace function rpad_upto(text, int) returns text as $$
begin
if length($1) >= $2 then
return $1;
end if;
return rpad($1, $2);
end;
$$ language plpgsql;
or this:
create or replace function rpad_upto(text, int) returns text as $$
select $1 || repeat(' ', $2 - length($1));
$$ language sql;
Then you can say things like:
select rpad_upto(colname, 30) from mytable ...
You might want to consider what you want rpad_upto(null, n) to produce while you're at it. Both versions of rpad_upto above will return NULL if $1 is NULL but you can tweak them to return something else without much difficulty.

Answer 3

how about this
select case when length(col) < x then rpad(col, x)
else col
end
from table

Answer 4

Assuming efficiency is not your biggest concern here:
select regexp_replace(format('%5s', 'foo'), '(\s*)(\S*)', '\2\1')
format() left-pads the string to the desired width
then regexp_replace moves any leading spaces to the end.
I guess that would fail if you have leading spaces in the strings and you want to preserve them. Also note that format() doesn't return null on null params.

Answer 5

PostgreSQL statement below is to right pad three place values and alter column data type to text for column 'columnname.' I used pycharm IDE to help construct statement. The statement will pad with 000.
I have been looking for a while to solve the same issue, except for left pad and I thought I would share.
alter table 'schema.tablename' alter column 'columnname' type text using rpad('columnname'::text,3,'0')