Fix GH-20122: getColumnMeta() for JSON-column in MySQL

[nielsdos]

While at it, also add VECTOR.

[mvorisek]

While this is true, the behaviour is not 100% the same, for example encoding JSON field as JSON does not add quotes when the value is not a string.

repro: https://dbfiddle.uk/YilhsCEk

JSON type must be preserved

[nielsdos]

That's not possible because mariadb protocol does not make the distinction in its metadata

[mvorisek]

@vuvova do you have an idea if the distinction of a JSON field is somehow possible?

[nielsdos]

You can even try this in a MariaDB CLI session to see it's even stored like LONGTEXT:

MariaDB [(none)]> create database testdb;
Query OK, 1 row affected (0.000 sec)

MariaDB [(none)]> use testdb;
Database changed
MariaDB [testdb]> create table test(a JSON);
Query OK, 0 rows affected (0.032 sec)

MariaDB [testdb]> describe test;
+-------+----------+------+-----+---------+-------+
| Field | Type     | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| a     | longtext | YES  |     | NULL    |       |
+-------+----------+------+-----+---------+-------+
1 row in set (0.002 sec)

MariaDB [testdb]> 

[mvorisek]

MariaDB internally checks the JSON type like in https://github.com/MariaDB/server/blob/mariadb-12.1.1/sql/item_jsonfunc.cc#L1848.

Then I found https://github.com/MariaDB/server/blob/mariadb-12.1.1/sql/sql_type_json.h#L86 - is this really sent in the protocol?

[nielsdos]

While it's true that the format is sent over as "json", it sends LONGTEXT in its type field, making an exception to this and transforming this to JSON is lying. See also https://mariadb.com/docs/server/reference/data-types/string-data-types/json

[mvorisek]

In atk4/data we need to detect the type is JSON - can https://github.com/MariaDB/server/blob/mariadb-12.1.1/sql/sql_type_json.h#L86 be accessed right now or can it be make accessible either by returning JSON here or via some other extended field?

[mvorisek]

I would say "lying" would be correct here:

1. in MariaDB, when format=json is set (if and only if the type is JSON internally), the type is JSON in reality
2. in MySQL and MariaDB JSON is always exported as string (encoded JSON)
3. JSON type is supported by both MySQL and MariaDB

[kamil-tekiela]

As far as I know, there is no JSON datatype in MySQL protocol. Has something changed recently?

[nielsdos]

As far as I know, there is no JSON datatype in MySQL protocol. Has something changed recently?

The JSON type was introduced in Mysql 5.7.8: https://dev.mysql.com/doc/refman/5.7/en/json.html but it's mainly treated as a string.

[kamil-tekiela]

I cannot set up PDO_MYSQL testing environment for some reason, but I looked into this topic more and it seems I was confused before. The JSON type seems to be present in the protocol and so it can be reported as you showed. I think I confused it with ENUM.

This line can also be added in mysqli_fetch_field_types.phpt:

        MYSQLI_TYPE_JSON => array('JSON', '[]'),