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

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

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6 changes: 6 additions & 0 deletions ext/pdo_mysql/mysql_statement.c
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Original file line number Diff line number Diff line change
Expand Up @@ -748,6 +748,12 @@ static char *type_to_name_native(int type) /* {{{ */
PDO_MYSQL_NATIVE_TYPE_NAME(DATE)
#ifdef FIELD_TYPE_NEWDATE
PDO_MYSQL_NATIVE_TYPE_NAME(NEWDATE)
#endif
#ifdef FIELD_TYPE_VECTOR
PDO_MYSQL_NATIVE_TYPE_NAME(VECTOR)
#endif
#ifdef FIELD_TYPE_JSON
PDO_MYSQL_NATIVE_TYPE_NAME(JSON)
#endif
PDO_MYSQL_NATIVE_TYPE_NAME(TIME)
PDO_MYSQL_NATIVE_TYPE_NAME(DATETIME)
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33 changes: 33 additions & 0 deletions ext/pdo_mysql/tests/gh20122.phpt
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@@ -0,0 +1,33 @@
--TEST--
GH-20122 (getColumnMeta() for JSON-column in MySQL)
--EXTENSIONS--
pdo
pdo_mysql
--SKIPIF--
<?php
require __DIR__ . '/config.inc';
require __DIR__ . '/../../../ext/pdo/tests/pdo_test.inc';
PDOTest::skip();
?>
--FILE--
<?php
require __DIR__ . '/config.inc';
require __DIR__ . '/../../../ext/pdo/tests/pdo_test.inc';
$db = PDOTest::test_factory(__DIR__ . '/common.phpt');

$db->exec('CREATE TABLE test (bar JSON)');
$db->exec('INSERT INTO test VALUES("[]")');

$stmt = $db->query('SELECT * from test');
$meta = $stmt->getColumnMeta(0);

// Note: JSON is an alias for LONGTEXT on MariaDB!
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@mvorisek mvorisek Oct 11, 2025 •
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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
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That's not possible because mariadb protocol does not make the distinction in its metadata
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@vuvova do you have an idea if the distinction of a JSON field is somehow possible?
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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]>
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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?
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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
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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?
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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
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@vuvova do you have an idea if the distinction of a JSON field is somehow possible?

Yes, possible since 2020.
But only if the client sets MARIADB_CLIENT_EXTENDED_TYPE_INFO capability bit.
https://jira.mariadb.org/browse/MDEV-17832
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Thanks, I'll look into it.
echo $meta['native_type'], "\n";
?>
--CLEAN--
<?php
require __DIR__ . '/mysql_pdo_test.inc';
MySQLPDOTest::dropTestTable();
?>
--EXPECTF--
%r(JSON|LONGTEXT)%r
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