MySQL SUM json values grouped by json keys

Question

Is it possible to calculate sum of json values grouped by json keys?

Mysql version is 5.7.17 on Google cloud sql.

Example_1: A short exampl

Answer 1

Solution for Example_3:

DROP TABLE IF EXISTS jsondata;
CREATE TABLE jsondata (json JSON, col varchar(11));

INSERT INTO jsondata VALUES
('[{"key_name" : "key1", "key_value" : 1}, {"key_name" : "key2", "key_value" : 3}]', 'aaa'),
('[{"key_name" : "key1", "key_value" : 0}, {"key_name" : "key3", "key_value" : 2}]', 'bbb'),
('[{"key_name" : "key1", "key_value" : 50}, {"key_name" : "key2", "key_value" : 0}]', 'aaa');

DROP FUNCTION IF EXISTS json_sum_by_col;
CREATE FUNCTION json_sum_by_col(col varchar(100)) RETURNS JSON
BEGIN
    DECLARE i INT DEFAULT 0;
    DECLARE done INT DEFAULT FALSE;
    DECLARE select_values JSON;
    DECLARE temp_result JSON;
    DECLARE json_result JSON DEFAULT '[]';
    DECLARE temp_key varchar(11);
    DECLARE temp_value int;

    DECLARE curs CURSOR FOR SELECT json FROM jsondata WHERE jsondata.col = col;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;

    OPEN curs;
        read_loop: LOOP
            SET i = 0;
            FETCH curs INTO select_values;

            IF done THEN
              LEAVE read_loop;
            END IF;

            WHILE i < JSON_LENGTH(select_values) DO
                -- extract key and value for i element
                SET temp_key = JSON_EXTRACT(JSON_EXTRACT(select_values, CONCAT('$[',i,']')), '$.key_name');
                SET temp_value = JSON_EXTRACT(JSON_EXTRACT(select_values, CONCAT('$[',i,']')), '$.key_value');

                -- search json_result for key
                SET @search = JSON_SEARCH(json_result, 'one', JSON_UNQUOTE(temp_key));
                IF @search IS NOT NULL THEN
                    -- if exists add to existing value
                    SET @value_path = JSON_UNQUOTE(REPLACE(@search, 'name', 'value'));
                    SET temp_value = temp_value + JSON_EXTRACT(json_result, @value_path);
                    SET json_result = JSON_REPLACE(json_result, @value_path, temp_value);
                ELSE
                    -- else attach it to json_result
                    SET temp_result = JSON_OBJECT("key_name", JSON_UNQUOTE(temp_key), "key_value", temp_value);
                    SET json_result = JSON_INSERT(json_result, CONCAT('$[',JSON_LENGTH(json_result),']'), temp_result);
                END IF;

                SELECT i + 1 INTO i;
            END WHILE;
        END LOOP;
    CLOSE curs;

    RETURN json_result;
END;

SELECT col, json_sum_by_col(col) FROM jsondata GROUP BY col;

You can run it here