How to SELECT JSON data stored in as text

Question

I have to extract data from a MariaDB database where the owners have stored JSON data in varchar fields in the form:

   [-100, -18.3, -10.1, 2.2, 5.8, ...]

I would like to be able to select individual entries from each of these JSON encoded text fields.

I have been reading about the many features of JSON support in MariaDB and I have looked at many examples of how data can be stored as JSON in text fields, but they all would require changes to how the data is inserted and/or the schema.

I cannot change the DB in any way. I have ReadOnly access.

The owners of the DB are currently using MariaDB 10.0, but I may be able to get them to upgrade to 10.1

In short, given the following (very simple example), how can I select the 2nd element in the ‘data’ field?

I assume using the JSON features is the way to go (given all the data is JSON), but is there another way? Performance isn't all that important.

MariaDB [mtest]> show columns from cal from mtest;
+-------+--------------+------+-----+---------+-------+
| Field | Type         | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| data  | varchar(255) | YES  |     | NULL    |       |
+-------+--------------+------+-----+---------+-------+
1 row in set (0.00 sec)

MariaDB [mtest]> select * from cal;
+---------+
| data    |
+---------+
| [10.1,12.0,16.78,18.9] |
+---------+
1 row in set (0.00 sec)

Answer 1

If you can upgrade to 10.1 (from MariaDB 10.1.9) via CONNECT can use JsonGet_Real function.

Try:

MariaDB [_]> SELECT VERSION();
+-----------------+
| VERSION()       |
+-----------------+
| 10.1.14-MariaDB |
+-----------------+
1 row in set (0.00 sec)

MariaDB [_]> INSTALL SONAME 'ha_connect';
Query OK, 0 rows affected (0.01 sec)

MariaDB [_]> CREATE FUNCTION `jsonget_real` RETURNS REAL SONAME 'ha_connect.so';
Query OK, 0 rows affected (0.00 sec)

MariaDB [_]> DROP TABLE IF EXISTS `cal`;
Query OK, 0 rows affected, 1 warning (0.01 sec)

MariaDB [_]> CREATE TABLE IF NOT EXISTS `cal` (
    ->   `data` VARCHAR(255)
    -> );
Query OK, 0 rows affected (0.00 sec)

MariaDB [_]> INSERT INTO `cal`
    ->   (`data`)
    -> VALUES
    ->   ('[10.1,12.0,16.78,18.9]');
Query OK, 1 row affected (0.00 sec)

MariaDB [_]> SELECT `data` FROM `cal`;
+------------------------+
| data                   |
+------------------------+
| [10.1,12.0,16.78,18.9] |
+------------------------+
1 row in set (0.00 sec)

MariaDB [_]> SELECT `jsonget_real`(`data`, '[1]', 2) FROM `cal`;
+--------------------------------+
| jsonget_real(`data`, '[1]', 2) |
+--------------------------------+
|                          12.00 |
+--------------------------------+
1 row in set (0.00 sec)