postgresql - replace all instances of a string within text field

Question

In postgresql, how do I replace all instances of a string within a database column?

Say I want to replace all instances of cat with dog, fo

Answer 1

Here is an example that replaces all instances of 1 or more white space characters in a column with an underscore using regular expression -

select distinct on (pd)
regexp_replace(rndc.pd, '\\s+', '_','g') as pd
from rndc14_ndc_mstr rndc;