mysql(5.6及以下)解析json

#json解析函数       
DELIMITER $$

DROP FUNCTION IF EXISTS `json_extract_c`$$

CREATE FUNCTION `json_extract_c`(
details TEXT,
required_field VARCHAR (255)
) RETURNS TEXT CHARSET latin1
BEGIN
SET details = SUBSTRING_INDEX(details, "{", -1);
SET details = SUBSTRING_INDEX(details, "}", 1);
RETURN TRIM(
    BOTH '"' FROM SUBSTRING_INDEX(
        SUBSTRING_INDEX(
            SUBSTRING_INDEX(
                details,
                CONCAT(
                    '"',
                    SUBSTRING_INDEX(required_field,'$.', -1),
                    '":'
                ),
                -1
            ),
            ',"',
            1
        ),
        ':',
        -1
    )
) ;
END$$
DELIMITER ;

example：
select json_extract_c(json, "$.totalDays"), json from item limit 100;