REGEXP_EXTRACT

Description

This is a function used to perform a regular match on a given string STR and extract the POS-th matching part that conforms to the specified pattern. For the function to return a matching result, the pattern must exactly match some part of the STR.

If no match is found, an empty string will be returned. It should be noted that when handling character set matching, Utf-8 standard character classes should be used. This ensures that functions can correctly identify and process various characters from different languages.

The str parameter is of 'string' type, representing the string to be subjected to regular matching. The pattern parameter is of 'string' type, representing the target regular expression pattern. The pos parameter is of 'integer' type, used to specify the position in the string from which to start searching for the regular expression match. The position starts from 1, and this parameter must be specified.

If the pattern is not allowed regexp regular,throw error;

Support character match classes : https://github.com/google/re2/wiki/Syntax

Syntax

REGEXP_EXTRACT(<str>, <pattern>, <pos>)

Parameters

Parameter	Description
<str>	The column that needs to undergo regular matching. It is of 'string' type.
<pattern>	The target regular expression pattern. It is of 'string' type.
<pos>	The parameter used to specify the position in the string from which to start searching for the regular expression match. It is an integer value representing the character position in the string (starting from 1). pos must be specified.

Return Value

The matching part of the pattern. It is of Varchar type. If no match is found, an empty string will be returned.

Example

Extract the first matching part.In this example, the regular expression ([[:lower:]]+)C([[:lower:]]+) matches the part of the string where one or more lowercase letters are followed by 'C' and then one or more lowercase letters. The first capturing group ([[:lower:]]+) before 'C' matches 'b', so the result is 'b'.

mysql> SELECT regexp_extract('AbCdE', '([[:lower:]]+)C([[:lower:]]+)', 1);
+-------------------------------------------------------------+
| regexp_extract('AbCdE', '([[:lower:]]+)C([[:lower:]]+)', 1) |
+-------------------------------------------------------------+
| b                                                           |
+-------------------------------------------------------------+

Extract the second matching part.Here, the second capturing group ([[:lower:]]+) after 'C' matches 'd', so the result is 'd'.

mysql> SELECT regexp_extract('AbCdE', '([[:lower:]]+)C([[:lower:]]+)', 2);
+-------------------------------------------------------------+
| regexp_extract('AbCdE', '([[:lower:]]+)C([[:lower:]]+)', 2) |
+-------------------------------------------------------------+
| d                                                           |
+-------------------------------------------------------------+

Match Chinese characters.The pattern (\p{Han}+)(.+) first matches one or more Chinese characters (\p{Han}+) and then matches the remaining part of the string ((.+)). The second capturing group matches the non - Chinese part of the string, so the result is 'This is a passage in English 1234567'.

mysql> select regexp_extract('这是一段中文 This is a passage in English 1234567', '(\\p{Han}+)(.+)', 2);
+-----------------------------------------------------------------------------------------------+
| regexp_extract('这是一段中文 This is a passage in English 1234567', '(\p{Han}+)(.+)', 2)       |
+-----------------------------------------------------------------------------------------------+
| This is a passage in English 1234567                                                          |
+-----------------------------------------------------------------------------------------------+

Insert variable values and perform matching.This example inserts data into a table and then uses the REGEXP_EXTRACT function to extract matching parts from the stored strings based on the stored patterns and positions.

CREATE TABLE test_table_for_regexp_extract (
        id INT,
        text_data VARCHAR(500),
        pattern VARCHAR(100),
        pos INT
    ) PROPERTIES ("replication_num"="1");

INSERT INTO test_table_for_regexp_extract VALUES
    (1, 'AbCdE', '([[:lower:]]+)C([[:lower:]]+)', 1),    
    (2, 'AbCdE', '([[:lower:]]+)C([[:lower:]]+)', 2),    
    (3, '这是一段中文 This is a passage in English 1234567', '(\\p{Han}+)(.+)', 2);

SELECT id, regexp_extract(text_data, pattern, pos) as extract_result FROM test_table_for_regexp_extract ORDER BY id;

+------+----------------+
| id   | extract_result |
+------+----------------+
|    1 | b              |
|    2 | d              |
|    3 | This is a passage in English 1234567 |
+------+----------------+

Test with a pattern that has no match.Since the pattern ([[:digit:]]+) (one or more digits) does not match any part of the string 'AbCdE', an empty string is returned.

SELECT regexp_extract('AbCdE', '([[:digit:]]+)', 1);

+------------------------------------------------+
| regexp_extract('AbCdE', '([[:digit:]]+)', 1)  |
+------------------------------------------------+
|                                                |
+------------------------------------------------+

Emoji test case

SELECT regexp_extract('Text 😊 More 😀', '😊|😀',0);

+------------------------------------------------------+
| regexp_extract('Text 😊 More 😀', '😊|😀',0)                 |
+------------------------------------------------------+
| 😊                                                     |
+------------------------------------------------------+

'str' is NULL, return NULL

mysql> SELECT REGEXP_EXTRACT(NULL, '([a-z]+)', 1);
+-------------------------------------+
| REGEXP_EXTRACT(NULL, '([a-z]+)', 1) |
+-------------------------------------+
| NULL                                |
+-------------------------------------+

'pattern' is NULL,return NULL

mysql> SELECT REGEXP_EXTRACT('Hello World', NULL, 1);
+----------------------------------------+
| REGEXP_EXTRACT('Hello World', NULL, 1) |
+----------------------------------------+
| NULL                                   |
+----------------------------------------+

'pos' is NULL,return NULL

mysql> SELECT REGEXP_EXTRACT('Hello World', '([a-z]+)', NULL);
+-------------------------------------------------+
| REGEXP_EXTRACT('Hello World', '([a-z]+)', NULL) |
+-------------------------------------------------+
| NULL                                            |
+-------------------------------------------------+

All parameters are NULL,return NULL

mysql> SELECT REGEXP_EXTRACT(NULL, NULL, NULL);
+----------------------------------+
| REGEXP_EXTRACT(NULL, NULL, NULL) |
+----------------------------------+
| NULL                             |
+----------------------------------+

If the pattern is not allowed regexp regular,throw error;

SELECT regexp_extract('AbCdE', '([[:digit:]]+', 1);

ERROR 1105 (HY000): errCode = 2, detailMessage = (10.16.10.2)[INVALID_ARGUMENT]Could not compile regexp pattern: ([[:digit:]]+
Error: missing ): ([[:digit:]]+