Question

I have values like this:
aaa_1, bb_5, c_21, a_b.
Now i need remove trailing underscore and numbers from this values. A_b (string_string) is valid value and need not to be removed. Basicaly, i need regexp patern to extract only trailing _[any number of digits] from string.

I am using Oracle 11gR2

Any suggestion?

Answer 1

You need to use REGEXP_REPLACE with the regex expression ‘\_[[:digit:]]{1,}’

This translates to find the (escaped) underscore with one or more digits after it:

e.g.

SELECT REGEXP_REPLACE('a_b', '\_[[:digit:]]{1,}'),
       REGEXP_REPLACE('aaa_1', '\_[[:digit:]]{1,}'),
       REGEXP_REPLACE('c_21', '\_[[:digit:]]{1,}'),
       REGEXP_REPLACE('bb_5', '\_[[:digit:]]{1,}')
  FROM dual;

Returns

a_b
aaa
c
bb

If you want to make sure you only remove the underscore and digits when there are no alpha characters then add the $ to the end of the regex string to signify the end of the string.

e.g. First with the “$” second without

SELECT REGEXP_REPLACE('bb_5b', '\_[[:digit:]]{1,}$'),
       REGEXP_REPLACE('bb_5b', '\_[[:digit:]]{1,}'),
       REGEXP_REPLACE('bb_55', '\_[[:digit:]]{1,}$'),
       REGEXP_REPLACE('bb_55', '\_[[:digit:]]{1,}')
  FROM dual;

Returns

bb_5b
bbb
bb
bb

Regular expressions can be awkward but this link is one of the easiest to understand that I have found for Oracle regex expressions:
http://www.dba-oracle.com/t_regular_expressions.htm

Hope this helps.