Oracle regular expression match string from last occurence - sql

Question

I'm still learning regexp in oracle and stuck with below error. Below is my sample code
SELECT DISTINCT COALESCE(TO_NUMBER(regexp_substr(USERNAME, '[^.]+', 1, 2)), ID) ID ,
COALESCE(regexp_substr(USERNAME, '[^.]+', 1, 1), USERNAME) AS USERNAME
FROM logs;
ORA-01722: invalid number
01722. 00000 - "invalid number"
*Cause: The specified number was invalid.
*Action: Specify a valid number.
Table Data
Username ID
Ravi.1234 1234
Krishna.12345 12345
Ravi.Krishna.1234567 1234567
R.Krishna.987 987
Ravi.K.567890 567890
R.Krish 123
Ravi 456
Expected Output
ID Username
1234 Ravi
12345 Krishna
1234567 Ravi.Krishna
987 R.Krishna
567890 Ravi.K
How to reframe the query to get the output needed. Can substr be used instead of regexp will it give desired output? This is used in oracle database not in sql. Thanks in advance.

Answer 1

If I understood your assignment correctly (see my comments under your question), here is how you can do this with standard string functions and conditions:
with
table_data (username, id) as (
select 'Ravi.1234' , '1234' from dual union all
select 'Krishna.12345' , '12345' from dual union all
select 'Ravi.Krishna.1234567', '1234567' from dual union all
select 'R.Krishna.987' , '987' from dual union all
select 'Ravi.K.567890' , '567890' from dual union all
select 'R.Krish' , '123' from dual union all
select 'Ravi' , '456' from dual
)
select id, substr(username, 1, instr(username, '.', -1) - 1) as username
from table_data
where username like '%.' || id
;
ID USERNAME
------- --------------------
1234 Ravi
12345 Krishna
1234567 Ravi.Krishna
987 R.Krishna
567890 Ravi.K
In the LIKE condition in the WHERE clause, % is a wildcard for "any string of any length, including zero"; that must be followed by a literal dot and then by the ID, and that must be the whole USERNAME string. In select, instr(username, '.', -1) finds the position of the "first" dot in username, but counting from the end and moving left - that is what the minus sign means.
With regular expression functions and conditions:
select id, regexp_substr(username, '^(.*)\.' || id || '$', 1, 1, null, 1) as username
from table_data
where regexp_like(username, '\.' || id || '$')
;
The sixth argument to regexp_substr means "the first substring enclosed in parentheses" (first "capture group" is the technical term).

Answer 2

I think REGEXP_REPLACE() would suit well for your case while filtering out the values having at least one digit. In the current case, you're trying to convert the second portions of the Username strings to number, but not all of them are numeric, the error raises due to this. Moreover, you can also extract the ID column from Username column. e.g. no need to hold seperate ID column within your original table.
Thus, consider using
SELECT TO_NUMBER( REGEXP_REPLACE(Username, '[^0-9]+') ) AS ID,
RTRIM( REGEXP_REPLACE(Username, '[^.]+$'),'.') AS "Username"
FROM logs
WHERE REGEXP_LIKE(Username,'[0-9]')
the following option would be an alternative to above one by using less Regular expression
SELECT TO_NUMBER( SUBSTR( Username, INSTR(Username, '.',-1)+1, LENGTH( Username ) )) AS ID,
SUBSTR( Username, 1, INSTR(Username, '.',-1)-1 ) AS "Username"
FROM logs
WHERE REGEXP_LIKE(Username,'[0-9]')
Demo