Fix GH-20122: getColumnMeta() for JSON-column in MySQL - #20143

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

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

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

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]> 

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?

Okay got it, thanks for the info

The implementation of the string change should still only be done on master. So I'll make a reminder issue to implement sending the flag + incorporating the string MariaDB sends us.

If this is going to be changed for MySQL, I do not see any reason to not change it for MariaDB. It is more or less transport protocol detail.

I consider this as a bug as JSON type is present almost in every DB since about y2020 and the type info is important to handle the data correctly, as reproduced above.

The JSON type was absent on both MariaDB & MySQL.
Other types may change if we send the flag and use the string the server sends back. This part is the BC break.

In PHP it shouldn't replace the old information, it should be presented as additional information too. If it is to replace the native type then it should be behind a user facing option and disabled by default.