Regexp_replace to remove blank lines from multi lines in a single field

Question

Gents. 10g R2.
   with test_tab as
   (select 'x'||chr(10)||'y'||chr(10)||chr(10)||'z' tester from dual)
   select tester from test_tabproduces
x
y
zI require
x
y
zThere's a lot of examples on how to end up with xzy, but I need to maintain the carriage returns, just strip out blank lines.
I've been trying with posix [:cntrl:] but it doesn't seem to want to work. Question: how to get the desired output?
If this has been answered on another post, please point me in the right direction and accept my apologies!

Answer 1

Hi,
The simplest thing might be to use LTRIM. (or TRIM, if you need to remove them from the end of the string, as well).
If you want a regular expression:
SELECT     REGEXP_REPLACE ( tester
                 , '(^|' || CHR (10) || ')' || CHR (10) || '+'
                 , '\1'
FROM     test_tab
;This might be easier to understand if you let x stand for CHR (10):
SELECT     REGEXP_REPLACE ( tester
                 , '(^|x)x+'
                 , '\1'
FROM     test_tab
;This is easier to understand: \1 is either the beginning of the string or x. When this is followed imeediately by 1 or more extra x's, then replace that whole pattern with \1 (that is, remove the extra x's).