How to extract group from regular expression in Oracle?

sql

regex

pattern-matching

string-extraction

byAnton Shumikhin·Oct 21, 2024

The Oracle function REGEXP_SUBSTR is your secret weapon for group extraction in a string. Here's the general syntax:

SELECT REGEXP_SUBSTR(source_column, 'your_regex(pick_group)', 1, 1, NULL, 2) as match
FROM source_table;

Your task is to replace source_column with the desired column, source_table with the table identifier, your_regex with the overall regex pattern, and pick_group with the group you want to extract. The 2 indicates the position of the group within your regex.

Deep-dive into group extraction

Extraction in Oracle 11g+

In Oracle 11g and later versions, the sixth parameter in REGEXP_SUBSTR function helped us to extract a specific capture group from the matched string. This gave us an upper hand in not only matching patterns but also isolating them.

SELECT REGEXP_SUBSTR('FindThis(InHere)','(.+)\((.+)\)', 1, 1, NULL, 2) AS CapturedGroup FROM DUAL;

The output will be InHere, which is the second group and specified by the final parameter. This select statement just saved your day!

Oracle 10g - The Twilight Years

For Oracle 10g and previous versions, owing to the absence of a capture group option, bunch up the string extraction and cutting tasks. This is achieved using a combo of REGEXP_SUBSTR and SUBSTR or any other string processing function.

Getting around the brackets

Handling brackets is an integral part of regex, so let's tame these tiny monsters! For stripping the brackets after extraction, ensure to trim them or adjust the regex pattern to avoid these brackets in the first place. Make RTRIM and LTRIM your partners for this task.

SELECT RTRIM(LTRIM(REGEXP_SUBSTR(source_column, '\[(.+)\]', 1, 1, NULL, '1'), '['), ']') as match
FROM source_table;

Don't forget to test it with different bracketed values, because testing is caring!

Visualization

To imagine it in another way, consider the process of extraction as receiving your letter from Hogwarts, the only hitch being that you need to extract your name from a pile of mail:

| SQL Snitch (🔮)   | Letter Pile(✉️)  | Name Tag (🔖) | Your Letter (📜) |
|------------------|-------------------|--------------|------------------|
| REGEXP_SUBSTR   | Source String     | Regex Group  | Extracted Value  |

Chip off the old block: Using regexp_replace

When you need to erase or replace certain parts of a string based on a pattern, give REGEXP_REPLACE a shot.

Replace like a pro

For example, you need to replace the content within brackets with a clever string "CONTENT". Here's how you can do it:

SELECT REGEXP_REPLACE(source_column, '\[(.+)\]', 'CONTENT') as updated_text
FROM source_table;

And yes, the brackets woke up and chose violence, but they met with REGEXP_REPLACE!

Crafting the perfect pattern

To let REGEXP_REPLACE and REGEXP_SUBSTR work their magic, fine-tune your patterns. Overly broad patterns might invite unwanted guests, while too narrow ones might miss the party. Make sure your regex invitation reaches the right crowd!

Handle Big Data with care

Remember that complex regular expressions can be a resource hog on large datasets. Optimize your pattern for efficiency and always have an eye on the performance impact.