mariadb_schema

This system database contains crucial metadata about the server, including information schema, statistics, and optimizer hints, for internal operations.

mariadb_schema was introduced in MariaDB 10.3.24, MariaDB 10.4.14 and MariaDB 10.5.5.

mariadb_schema is a data type qualifier that allows one to create MariaDB native date types in an SQL_MODE that has conflicting data type translations.

In SQL_MODE=ORACLE, if you create a table with the DATE type, it actually creates a DATETIME column to match what an Oracle user is expecting. To be able to create a MariaDB DATE in Oracle mode, you would have to use mariadb_schema:

CREATE TABLE t1 (d mariadb_schema.DATE);

mariadb_schema is also shown if you create a table with DATE in MariaDB native mode and then do a SHOW CREATE TABLE in ORACLE mode:

SET sql_mode=DEFAULT;
CREATE OR REPLACE TABLE t1 (
  d DATE
);
SET SQL_mode=ORACLE;
SHOW CREATE TABLE t1;
+-------+--------------------------------------------------------------+
| Table | Create Table                                                 |
+-------+--------------------------------------------------------------+
| t1    | CREATE TABLE "t1" (
  "d" mariadb_schema.DATE DEFAULT NULL
) |
+-------+--------------------------------------------------------------+

When the server sees the mariadb_schema qualifier, it disables sql_mode-specific data type translation and interprets the data type literally, so for example mariadb_schema.DATE is interpreted as the traditional MariaDB DATE data type, no matter what the current SQL mode is.

The mariadb_schema prefix is displayed only when the data type name would be ambiguous otherwise. The prefix is displayed together with MariaDB DATE when SHOW CREATE TABLE is executed in SQL_MODE=ORACLE. The prefix is not displayed when SHOW CREATE TABLE is executed in SQL_MODE=DEFAULT, or when a non-ambiguous data type is displayed.

The mariadb_schema prefix can be used with any data type, including non-ambiguous ones.

CREATE OR REPLACE TABLE t1 (a mariadb_schema.INT);
SHOW CREATE TABLE t1;
+-------+--------------------------------------------------+
| Table | Create Table                                     |
+-------+--------------------------------------------------+
| t1    | CREATE TABLE "t1" (
  "a" INT(11) DEFAULT NULL
) |
+-------+--------------------------------------------------+

The mariadb_schema prefix is only used in the following case:

• For a MariaDB native DATE type when running SHOW CREATE TABLE in Oracle mode.

History

When running with SQL_MODE=ORACLE, MariaDB server translates the data type DATE to DATETIME, for better Oracle compatibility:

SET SQL_mode=ORACLE;
CREATE OR REPLACE TABLE t1 (
  d DATE
);
SHOW CREATE TABLE t1;
+-------+---------------------------------------------------+
| Table | Create Table                                      |
+-------+---------------------------------------------------+
| t1    | CREATE TABLE "t1" (
  "d" datetime DEFAULT NULL
) |
+-------+---------------------------------------------------+

Notice, DATE was translated to DATETIME.

This translation may cause some ambiguity. Suppose you create a table with a column of the traditional MariaDB DATE data type using the default SQL mode, but then switche to SQL_MODE=ORACLE and run a SHOW CREATE TABLE statement:

SET sql_mode=DEFAULT;
CREATE OR REPLACE TABLE t1 (
  d DATE
);
SET SQL_mode=ORACLE;
SHOW CREATE TABLE t1;

Before mariadb_schema was introduced, the above script displayed:

CREATE TABLE "t1" (
  "d" DATE DEFAULT NULL
);

This had two problems:

• It was confusing for the reader: its not clear if it is the traditional MariaDB DATE, or is it Oracle-alike date (which is actually DATETIME);

• It broke replication and caused data type mismatch on the master and on the slave (see MDEV-19632).

To address this problem, starting from the mentioned versions, MariaDB uses the idea of qualified data types:

SET sql_mode=DEFAULT;
CREATE OR REPLACE TABLE t1 (
  d DATE
);
SET SQL_mode=ORACLE;
SHOW CREATE TABLE t1;
+-------+--------------------------------------------------------------+
| Table | Create Table                                                 |
+-------+--------------------------------------------------------------+
| t1    | CREATE TABLE "t1" (
  "d" mariadb_schema.DATE DEFAULT NULL
) |
+-------+--------------------------------------------------------------+

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