How to use Oracle regular expressions to extract strings.

You can use the Oracle regular expression function regexp_substr to extract substrings. Here is an example demonstrating how to use this function to extract the numeric part of a string.

Assume you have a string containing both numbers and letters, such as ABC123DEF456GHI, and you want to extract only the numerical part.

You can achieve this by using the following SQL statement:

SELECT regexp_substr('ABC123DEF456GHI', '\d+') AS extracted_string
FROM dual;

The output will be 123, which is the first consecutive number sequence in the input string.

The regular expression \d+ here represents matching consecutive numbers. In the regexp_substr function, the first parameter is the string to be matched, and the second parameter is the regular expression pattern. Using FROM dual is a standard practice in Oracle to select data from the pseudotable dual in the system.

You can adjust the regular expression pattern and the matching string according to your needs to achieve the desired extraction effect.