Replaces multiple newlines into single one

newline.sql

with a as
(select q'{
 Line 1
 Line 2
 Line 3
 
 
 Line 4
    
 

 Line 5
}' l from dual
)
select regexp_replace(a.l,'('||CHR(10)||'[[:space:]]*'||CHR(10)||'){2,}',CHR(10)||CHR(10)) a 
  from a;

Assumes that new line is \n symbol. If it's \r\n, then replace CHR(10) with CHR(13)||CHR(10).