Read JSON array in MYSQL

Question

I'm unable to extract determinate data in a JSON.

I have this JSON:

[{"id":1, "type":2}, {"id":2, "type":1}]

I want to recover all the ids in a variable in my stored procedure.

CREATE DEFINER=`root`@`%` PROCEDURE `new_procedure`(a JSON)
BEGIN
   SELECT JSON_TYPE(a);
   -- return ARRAY

   SELECT a,JSON_EXTRACT(a,'$.id');
END

a return the JSON, but JSON_EXTRACT is empty

Even I prove to save the JSON in a temporary table

CREATE DEFINER=`root`@`%` PROCEDURE `new_procedure`(a JSON)
BEGIN

   SELECT JSON_TYPE(a);
   DROP TEMPORARY TABLE IF EXISTS jsonTemporary;

   CREATE TEMPORARY TABLE jsonTemporary SELECT a;

   SELECT *,a->'$.id',a->>'$.id',JSON_EXTRACT(a,'$.id') FROM jsonTemporary;
END

But the result is the same only the first column return something.

These are a real data. I don't have table, I want to read the JSON to work with the ids and types and then insert in a secondary table. — monchyrcg
– monchyrcg, Commented Sep 14, 2017 at 11:46

wchiquito · Accepted Answer · 2017-09-15 09:44:15Z

mysql> SET @`json` :=
    -> '[
    '>    {
    '>      "id": 1, "type": 2
    '>    },
    '>    {
    '>      "id": 2, "type": 1
    '>    }
    '> ]';
Query OK, 0 rows affected (0.00 sec)

You can get all ids in an array:

mysql> SELECT JSON_EXTRACT(@`json` ,'$[*].id');
+----------------------------------+
| JSON_EXTRACT(@`json` ,'$[*].id') |
+----------------------------------+
| [1, 2]                           |
+----------------------------------+
1 row in set (0.00 sec)

Can access each JSON id:

mysql> SELECT JSON_EXTRACT(@`json` ,'$[0].id');
+----------------------------------+
| JSON_EXTRACT(@`json` ,'$[0].id') |
+----------------------------------+
| 1                                |
+----------------------------------+
1 row in set (0.00 sec)

Try:

mysql> DROP PROCEDURE IF EXISTS `new_procedure`;
Query OK, 0 rows affected (0.00 sec)

mysql> DELIMITER //

mysql> CREATE PROCEDURE `new_procedure`(`json` JSON)
    -> BEGIN
    ->   DECLARE `json_items` BIGINT UNSIGNED DEFAULT JSON_LENGTH(`json`);
    ->   DECLARE `_index` BIGINT UNSIGNED DEFAULT 0;
    -> 
    ->   DROP TEMPORARY TABLE IF EXISTS `jsonTemporary`;
    -> 
    ->   CREATE TEMPORARY TABLE IF NOT EXISTS `jsonTemporary`
    ->     (`id` BIGINT UNSIGNED NOT NULL);
    -> 
    ->   WHILE `_index` < `json_items` DO
    ->     INSERT INTO `jsonTemporary` (`id`)
    ->     VALUES (JSON_EXTRACT(`json`, CONCAT('$[', `_index`, '].id')));
    ->     SET `_index` := `_index` + 1;
    ->   END WHILE;
    -> 
    ->   SELECT `id` FROM `jsonTemporary`;
    ->   DROP TEMPORARY TABLE IF EXISTS `jsonTemporary`;
    -> END//
Query OK, 0 rows affected (0.00 sec)

mysql> DELIMITER ;

mysql> CALL `new_procedure`(@`json`);
+----+
| id |
+----+
|  1 |
|  2 |
+----+
2 rows in set (0.00 sec)
Query OK, 0 rows affected (0.00 sec)

See db-fiddle.

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