Re: how can I replace all instances of a pattern

On 03/26/2013 06:08 AM, James Sharrett wrote:
> I'm trying remove all instances of non-alphanumeric or underscore
> characters from a query result for further use. This is part of a
> function I'm writing that is in plpgsql
>
> Examples:
>
> Original value
> 'My text1'
> 'My text 2'
> 'My-text-3'
> 'My_text4'
> 'My!text5'
>
> Desired
> 'Mytext1'
> 'Mytext2'
> 'Mytext3'
> 'My_text4' (no change)
> 'Mytext5'
>
>
> The field containing the text is column_name. I tried the following:
>
> Select regexp_replace(column_name,'\W','') from mytable
>
> This deals with the correct characters but only does the first
> instance of the character so the output is:
>
> 'My text1'
> 'Mytext 2' (wrong)
> 'Mytext-3' (wrong)
> 'My_text4'
> 'My!text5'
>
> I managed to get the desired output by writing the text into a
> variable through a loop and then just keep looping on the variable
> until all the characters are removed:
>
> sql_qry:= 'select column_name from mytable';
>
> for sql_record in execute sql_qry loop
> curr_record := sql_record.column_name;
>
> while length(substring(curr_record from '\W'))>0 loop
> curr_record := regexp_replace(curr_record, '\W','');
> end loop;
>
> .... rest of the code
>
> This works but it seems like a lot of work to do something this simple
> but I cannot find any function that will replace all instances of a
> string AND can base it on a regular expression pattern. Is there a
> better way to do this in 9.1?

You were on the right track with regexp_replace but you need to add a
global flag:
regexp_replace(column_name,'\W','','g')

See examples under
http://www.postgresql.org/docs/9.1/static/functions-matching.html#FUNCTIONS-POSIX-REGEXP

Cheers,
Steve