从 JSON 上的键和数组中提取值

Question

How could I extract the values in keys and array on json

json

{
    "key1": "US",
    "key2": "545644566",
    "car": ["HONDA","TOYOTA","FORD"]
}

The resulted expected:

key	value
key1	US
key2	545644566
car	HONDA
car	TOYOTA
car	FORD

I tried using:

SELECT JSON_EXTRACT(u.json, CONCAT('$.','"',g.field_name,'"')),g.*
  FROM table_json u
  LEFT JOIN table_column g 
    ON JSON_CONTAINS(JSON_KEYS(u.json), JSON_QUOTE(g.field_name), '$')

Answer 1

You can use a dictionary table such as information_schema.tables along with iterating index values for some variables in order to generate rows for the elements of the arrays. The following code also works for non-array elements without need of a conditional. Apply JSON_KEYS() function to derive the key elements in the first subquery, and then use JSON_EXTRACT() for the respective indexes to derive the corresponding values of the arrays in the last subquery such as

WITH t1 AS
(
SELECT @i := @i + 1 AS i, 
       JSON_UNQUOTE(JSON_EXTRACT(kys, CONCAT('$[', @i - 1, ']'))) AS `key`,
       JSON_EXTRACT(json,
                         CONCAT('$.',
                                      JSON_EXTRACT(kys, CONCAT('$[', @i - 1, ']'))
                                      )
                        ) AS value, kys
  FROM t
  JOIN (SELECT @i := 0, JSON_KEYS(json) AS kys FROM t) AS k
  JOIN information_schema.tables
)
SELECT @k := IF(@j=`key`,@k + 1,0) AS `index`,
       @j := `key` AS `key`,
       JSON_UNQUOTE(JSON_EXTRACT(value, CONCAT('$[', @k, ']'))) AS value
  FROM t1
  JOIN (SELECT @k := 0 ) AS k
  LEFT JOIN information_schema.tables
    ON @k < JSON_LENGTH(value) - 1
 WHERE value IS NOT NULL 

Demo