Oracle SQL - select parts of a string

Question

How can I select abcdef.txt from the following string?

abcdef.123.txt

I only know how to select abcdef by doing select substr('abcdef.123.txt',1,6) from dual;

Answer 1

You can using || for concat and substr -3 for right part

select substr('abcdef.123.txt',1,6)  || '.' ||substr('abcdef.123.txt',-3) from dual;

or avoiding a concat (like suggested by Luc M)

select substr('abcdef.123.txt',1,7)   || substr('abcdef.123.txt',-3) from dual;

Answer 2

A general solution, assuming the input string has exactly two periods . and you want to extract the first and third tokens, separated by one . The length of the "tokens" in the input string can be arbitrary (including zero!) and they can contain any characters other than .

select regexp_replace('abcde.123.xyz', '([^.]*).([^.]*).([^.]*)', '\1.\3') as result
  from dual;

RESULT
---------
abcde.xyz

Explanation:

• [ ] means match any of the characters between brackets .
• ^ means do NOT match the characters in the brackets - so...
• [^.] means match any character OTHER THAN .
• * means match zero or more occurrences, as many as possible ( "greedy" match)
• ( ... ) is called a subexpression ... see below
• '\\1.\\3 means replace the original string with the first subexpression, followed by . , followed by the THIRD subexpression .

Answer 3

Replace the substring of anything surrounded by dots (inclusive) with a single dot. No dependence on lengths of components of the string:

SQL> select regexp_replace('abcdef.123.txt', '\..*\.', '.') fixed
     from dual;

FIXED
----------
abcdef.txt

SQL>