JSON Data Type

The JSON alias was added to make it possible to use JSON columns in statement based replication from MySQL to MariaDB and to make it possible for MariaDB to read mysqldumps from MySQL.

JSON is an alias for LONGTEXT introduced for compatibility reasons with MySQL's JSON data type. MariaDB implements this as a LONGTEXT rather, as the JSON data type contradicts the SQL standard, and MariaDB's benchmarks indicate that performance is at least equivalent.

In order to ensure that a a valid json document is inserted, the JSON_VALID function can be used as a CHECK constraint. This constraint is automatically included for types using the JSON alias from MariaDB 10.4.3.



| Field | Type     | Null | Key | Default | Extra |
| j     | longtext | YES  |     | NULL    |       |

With validation:

  j JSON 

INSERT INTO t2 VALUES ('invalid');
ERROR 4025 (23000): CONSTRAINT `j` failed for `test`.`t2`

INSERT INTO t2 VALUES ('{"id": 1, "name": "Monty"}');
Query OK, 1 row affected (0.13 sec)

Replicating JSON Data Between MySQL and MariaDB

The JSON type in MySQL stores the JSON object in a compact form, not as LONGTEXT as in MariaDB. This means that row based replication will not work for JSON types from MySQL to MariaDB.

There are a a few different ways to solve this:

  • Use statement based replication.
  • Change the JSON column to type TEXT in MySQL
  • If you must use row-based replication and cannot change the MySQL master from JSON to TEXT, you can try to introduce an intermediate MySQL slave and change the column type from JSON to TEXT on it. Then you replicate from this intermediate slave to MariaDB.

Converting a MySQL TABLE with JSON Fields to MariaDB

MariaDB can't directly access MySQL's JSON format.

There are a a few different ways to move the table to MariaDB:

Differences Between MySQL JSON Strings and MariaDB JSON Strings

  • In MySQL, JSON is an object and is compared according to json values. In MariaDB JSON strings are normal strings and compared as strings. One exception is when using JSON_EXTRACT() in which case strings are unescaped before comparison.

See Also


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