Silent Column Changes

Explore Silent Column Changes in MariaDB. Learn when the server automatically modifies column definitions or data types during table creation to ensure engine compatibility.

When a CREATE TABLE or ALTER TABLE command is issued, MariaDB silently changes a column specification in the following cases:

• PRIMARY KEY columns are always NOT NULL.

• Any trailing spaces from SET and ENUM values are discarded.

• TIMESTAMP columns are always NOT NULL, and display sizes are discarded.

• A row-size limit of 65535 bytes applies.

• If strict SQL mode is not enabled (by default, it is), a VARCHAR column longer than 65535 become TEXT, and a VARBINARY columns longer than 65535 becomes a BLOB. If strict mode is enabled the silent changes will not be made, and an error will occur.

• If a USING clause specifies an index that's not permitted by the storage engine, the engine will instead use another available index type that can be applied without affecting results.

• If the CHARACTER SET binary attribute is specified, the column is created as the matching binary data type. A TEXT becomes a BLOB, CHAR a BINARY and VARCHAR a VARBINARY. ENUMs and SETs are created as defined.

To ease imports from other RDBMSs, MariaDB also silently maps the following data types:

Other Vendor Type	MariaDB Type
BOOL	TINYINT
BOOLEAN	TINYINT
CHARACTER VARYING(M)	VARCHAR(M)
FIXED	DECIMAL
FLOAT4	FLOAT
FLOAT8	DOUBLE
INT1	TINYINT
INT2	SMALLINT
INT3	MEDIUMINT
INT4	INT
INT8	BIGINT
LONG VARBINARY	MEDIUMBLOB
LONG VARCHAR	MEDIUMTEXT
LONG	MEDIUMTEXT
MIDDLEINT	MEDIUMINT
NUMERIC	DECIMAL

Currently, all MySQL types are supported in MariaDB.

For type mapping between Cassandra and MariaDB, see Cassandra storage engine.

Example

Silent changes in action:

CREATE TABLE SilenceIsGolden
   (
    f1 TEXT CHARACTER SET BINARY,
    f2 VARCHAR(15) CHARACTER SET BINARY,
    f3 CHAR CHARACTER SET BINARY,
    f4 ENUM('x','y','z') CHARACTER SET BINARY,
    f5 VARCHAR (65536),
    f6 VARBINARY (65536),
    f7 INT1
   );
Query OK, 0 rows affected, 2 warnings (0.31 sec)

SHOW WARNINGS;
+-------+------+-----------------------------------------------+
| Level | Code | Message                                       |
+-------+------+-----------------------------------------------+
| Note  | 1246 | Converting column 'f5' from VARCHAR to TEXT   |
| Note  | 1246 | Converting column 'f6' from VARBINARY to BLOB |
+-------+------+-----------------------------------------------+

DESCRIBE SilenceIsGolden;
+-------+-------------------+------+-----+---------+-------+
| Field | Type              | Null | Key | Default | Extra |
+-------+-------------------+------+-----+---------+-------+
| f1    | blob              | YES  |     | NULL    |       |
| f2    | varbinary(15)     | YES  |     | NULL    |       |
| f3    | binary(1)         | YES  |     | NULL    |       |
| f4    | enum('x','y','z') | YES  |     | NULL    |       |
| f5    | mediumtext        | YES  |     | NULL    |       |
| f6    | mediumblob        | YES  |     | NULL    |       |
| f7    | tinyint(4)        | YES  |     | NULL    |       |
+-------+-------------------+------+-----+---------+-------+

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