grep-like query for postgres - regex

Question

With the ~ operator, it is simple to find all lines in a table for which a column matches a given regexp pattern :
SELECT description from book where description ~ 'hell?o'
matches lines containing hello or helo
Instead of the description, I would like to SELECT a snippet of text around each occurences of the pattern, so if a line contains
description = "aaaheloaaabbbhellobbbcccheloccc"
I would like 3 lines as output :
"aaaheloaaa"
"bbbhellobbb"
"cccheloccc"
which I call a "grep-like" query because it can show extracts of the column where the match is found.

Answer 1

Try something like:
SELECT
regexp_matches(description,'(.{0,3})('||'hell?o'||')(.{0,3})','g')
FROM
book
WHERE description ~ 'hell?o'
Without the WHERE clause you will get null in rows, where were no matches for regexp.

Answer 2

I think you need the regexp_split_to_table function:
http://www.postgresql.org/docs/current/static/functions-matching.html
And you can use it like this:
SELECT foo FROM regexp_split_to_table('the quick brown fox jumped over the lazy dog', E'\\s+') AS foo;
The return:
foo
--------
the
quick
brown
fox
jumped
over
the
lazy
dog
(9 rows)
So in your case this would look like:
select res from book, regexp_split_to_table(book.description, E'...hell?o...') res;