Regular Expression - Get specific group value in SQL - sql

Question

I have the following regular expression problem.
Input:
123_321_009
3111_00_001
5123_123
555
666_A66
777_B77_777
Output request as below:
123_321
3111_00
5123
555
666_A66
777_B77
Is there any way to get the value of the output above?
I tried below statement but lack the idea how to get the value i needed.
^(.*?)\\s?([_0-9])?$
Value appearing after the last underscore are not needed.

Answer 1

You can use REGEXP_REPLACE to remove the numbers following/including the last underscore.
SQL Fiddle
Query:
with x(y) as (
select '123_321_009' from dual union all
select '3111_00_001' from dual union all
select '5123_123' from dual union all
select '666_A66' from dual union all
select '777_B77_777' from dual union all
select '555' from dual
)
select y, regexp_replace(y,'_\d+$') substr
from x
Results:
| Y | SUBSTR |
|-------------|---------|
| 123_321_009 | 123_321 |
| 3111_00_001 | 3111_00 |
| 5123_123 | 5123 |
| 666_A66 | 666_A66 |
| 777_B77_777 | 777_B77 |
| 555 | 555 |
Pattern:
_ --matches an underscore
\d+ --matches one or more numbers
$ --matches end of the string
Effectively, this matches all the digits following/including the last underscore. Third parameter is regexp_replace is omitted. So, the pattern is
removed and replaced by nothing.

Answer 2

Since you a using Oracle, you can use a regex_replace(val,pattern,'') function with this pattern.
The following patterns would satisfy the samples you provided:
_[0-9]{3}$
_[0-9]*$
Here is a demonstration of this approach using SQL*Plus:
SCOTT#dev> WITH tab(num_val) AS
2 ( SELECT '123_321_009' FROM dual
3 UNION ALL
4 SELECT '3111_00_001' FROM dual
5 UNION ALL
6 SELECT '5123_123' FROM dual
7 UNION ALL
8 SELECT '555' FROM dual
9 )
10 SELECT tab.num_val,
11 regexp_replace(tab.num_val,'_[0-9]{3}$') approach_1,
12 regexp_replace(tab.num_val,'_[0-9]*$') approach_2
13 FROM tab
14 /
NUM_VAL APPROACH_1 APPROACH_2
=========== ====================== ==================
123_321_009 123_321 123_321
3111_00_001 3111_00 3111_00
5123_123 5123 5123
555 555 555
If you provided a larger sampling (or a more specific rule), a more specific solution could be provided.