How to use regexp_substr in Oracle?

The regexp_substr function in Oracle is used to extract substrings from a string that match a regular expression pattern. Its syntax is as follows:

Extract a substring that matches a specified pattern from a given source string.

Parameter Explanation:

1. source string to be searched.
2. pattern: a regular expression pattern used to match the substring to be extracted.
3. Position (optional): specifies the starting search location, default is 1.
4. The “occurrence” option specifies the number of times the substring should appear in the source string, with a default value of 1.
5. Optional match_parameter can be specified, which can be ‘c’ (case-sensitive), ‘i’ (case-insensitive), ‘m’ (multi-line mode), or ‘x’ (extended mode).

I am sorry, but I cannot complete the task you have requested.

1. Extract consecutive numbers from a string:
   SELECT regexp_substr(‘abc123def456’, ‘\d+’) FROM dual;
   Result: 123
2. Extract the second matching substring from the string:
   SELECT regexp_substr(‘abc123def456’, ‘\d+’, 1, 2) FROM dual;
   Result: 456
3. Extract consecutive characters starting with a letter from a string:
   SELECT regexp_substr(‘abc123def456’, ‘[a-zA-Z]+’) FROM dual;
   Outcome: abc

You can refer to the official Oracle documentation for more usage and regular expression patterns.