MySQL regexp_substr() Function

The REGEXP_SUBSTR() function is used in MySQL to extract substrings from a string that match a specified regular expression pattern. This function is helpful when you want to extract specific portions of text from a larger string based on a pattern.

Here’s the basic syntax of the REGEXP_SUBSTR() function:

REGEXP_SUBSTR(string, pattern, [start_position], [occurrence], [modifier])

• string: The input string from which you want to extract substrings.
• pattern: The regular expression pattern you want to match.
• start_position (optional): The position within the string to start searching for the pattern. The default is 1.
• occurrence (optional): The occurrence of the pattern you want to match. The default is 1.
• modifier (optional): A regular expression modifier that affects how the pattern is interpreted.

Here’s an example usage of the REGEXP_SUBSTR() function in MySQL:

SELECT REGEXP_SUBSTR('Hello, world! This is a sample.', '[a-z]+')
-- Output: 'ello'

In this example, the function extracts the first sequence of lowercase letters from the input string.

Another example that demonstrates using optional parameters:

SELECT REGEXP_SUBSTR('apple, banana, cherry', '[a-z]+', 8, 2)
-- Output: 'banana'

In this case, the function starts searching from the 8th position and extracts the second occurrence of lowercase letters.

Remember that the usage of regular expressions in SQL can vary slightly between database systems. The REGEXP_SUBSTR() function is specific to MySQL. If you’re using a different relational database system, the function’s name or syntax might differ.