MySQL Regex pattern for ***.leave this.*** doesnt work - mysql

Question

What pattern to use to leave the characters between dots in string
"12395.KS_TH014.001239" so what would be left only "KS_TH014", if its dynamical var.
I tried pattern ".\K.*?(?=.)" but it doesnt work in mysql (mariadb 10.0.10 server)

Answer 1

There are no regex groups up and including mysql-5.7. However one can use UDF(user defined function) to achieve similar behavior:
SELECT REGEX_REPLACE(REGEX_CAPTURE_LEFTMOST('12395.KS_TH014.001239', '[[.period.]].*[[.period.]]'), '[[.period.]]', '');
The function below replaces the leftmost regex in a string:
DELIMITER $$
CREATE FUNCTION REGEX_REPLACE(var_original VARCHAR(1000), var_pattern VARCHAR(1000),
var_replacement VARCHAR(1000)) RETURNS VARCHAR(1000)
COMMENT 'Based on https://techras.wordpress.com/2011/06/02/regex-replace-for-mysql/'
BEGIN
DECLARE var_replaced VARCHAR(1000) DEFAULT var_original;
DECLARE var_leftmost_match VARCHAR(1000) DEFAULT
REGEX_CAPTURE_LEFTMOST(var_original, var_pattern);
WHILE var_leftmost_match IS NOT NULL DO
IF var_replacement <> var_leftmost_match THEN
SET var_replaced = REPLACE(var_replaced, var_leftmost_match, var_replacement);
SET var_leftmost_match = REGEX_CAPTURE_LEFTMOST(var_replaced, var_pattern);
ELSE
SET var_leftmost_match = NULL;
END IF;
END WHILE;
RETURN var_replaced;
END$$
DELIMITER ;
which depends on:
DELIMITER $$
CREATE FUNCTION REGEX_CAPTURE_LEFTMOST(var_original VARCHAR(1000), var_pattern VARCHAR(1000)) RETURNS VARCHAR(1000)
COMMENT '
Captures the leftmost substring that matches the [var_pattern]
IN [var_original], OR NULL if no match.
'
BEGIN
DECLARE var_temp_l VARCHAR(1000);
DECLARE var_temp_r VARCHAR(1000);
DECLARE var_left_trim_index INT;
DECLARE var_right_trim_index INT;
SET var_left_trim_index = 1;
SET var_right_trim_index = 1;
SET var_temp_l = '';
SET var_temp_r = '';
WHILE (CHAR_LENGTH(var_original) >= var_left_trim_index) DO
SET var_temp_l = LEFT(var_original, var_left_trim_index);
IF var_temp_l COLLATE utf8_unicode_ci REGEXP var_pattern COLLATE utf8_unicode_ci THEN
WHILE (CHAR_LENGTH(var_temp_l) >= var_right_trim_index) DO
SET var_temp_r = RIGHT(var_temp_l, var_right_trim_index);
IF var_temp_r COLLATE utf8_unicode_ci REGEXP var_pattern COLLATE utf8_unicode_ci THEN
RETURN var_temp_r;
END IF;
SET var_right_trim_index = var_right_trim_index + 1;
END WHILE;
END IF;
SET var_left_trim_index = var_left_trim_index + 1;
END WHILE;
RETURN NULL;
END$$
DELIMITER ;