how can I replace all instances of a pattern

[James Sharrett]

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?

[James Sharrett]

Sorry, caught a typo.  Mytext1 is correctly replaced because only one instance of the character (space) is in the string.

[k...@rice.edu]

Hi James,

Try adding the g flag to the regex (for global). From the documentation:

regexp_replace('foobarbaz', 'b..', 'X')
fooXbaz
regexp_replace('foobarbaz', 'b..', 'X', 'g')
fooXX
regexp_replace('foobarbaz', 'b(..)', E'X\\1Y', 'g')
fooXarYXazY

Regards,
Ken


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[Steve Crawford]

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

[James Sharrett]

Thanks Ken! I missed that option going through the documentation.