Delete a constrained column - ApsaraDB for OceanBase - Alibaba Cloud Documentation Center

This topic describes incompatibilities between MySQL databases and MySQL tenants of OceanBase Database when you delete a constrained column. The incompatibilities vary depending on the constraint.

Note

In the following tables, an empty cell in the type column indicates that the type is not supported by the corresponding constraint.

Delete a PRIMARY KEY column

The following table describes whether you can delete PRIMARY KEY columns of different types by executing the ALTER TABLE DDL statement in a MySQL database and a MySQL tenant of OceanBase Database.

Column type in a MySQL database	Deletion allowed	Column type in a MySQL tenant of OceanBase Database	Deletion allowed
INT	Yes	INTEGER	No
TINYINT	Yes	TINYINT	No
SMALLINT	Yes	SMALLINT	No
MEDIUMINT	Yes	MEDIUMINT	No
BIGINT	Yes	BIGINT	No
BOOL	Yes	BOOLEAN	No
DECIMAL	Yes	DECIMAL	No
NUMERIC	Yes	NUMERIC	No
REAL	Yes	FLOAT	No
DOUBLE	Yes	DOUBLE	No
FLOAT	Yes	FLOAT	No
BIT	Yes	BIT	No
CHAR	Yes	CHAR	No
NCHAR	Yes	CHAR	No
VARCHAR	Yes	VARCHAR	No
BINARY	Yes	BINARY	No
VARBINARY	Yes	VARBINARY	No
LONG VARBINARY	Yes
YEAR	Yes	YEAR	No
DATE	Yes	DATE	No
TIME	Yes	TIME	No
TIMESTAMP	Yes	TIMESTAMP	No
DATETIME	Yes	DATETIME	No
TINYBLOB	Yes
MEDIUMBLOB	Yes
BLOB	Yes
LONGBLOB	Yes
TINYTEXT	Yes
MEDIUMTEXT	Yes
TEXT	Yes
LONGTEXT	Yes
ENUM	Yes	ENUM	No
SET	Yes	SET	No
JSON	Yes (However, if a column is involved in a functional dependency, the column cannot be deleted.)

Delete a UNIQUE KEY column

If a UNIQUE KEY column is of a type described in the preceding table, the support for deleting the column by executing the ALTER TABLE DDL statement in a MySQL database and a MySQL tenant of OceanBase Database is the same as that for a PRIMARY KEY column.

Delete a KEY column

If a KEY column is of a type described in the preceding table, the support for deleting the column by executing the ALTER TABLE DDL statement in a MySQL database and a MySQL tenant of OceanBase Database is the same as that for a PRIMARY KEY column.

Delete a FULLTEXT indexed column

The following table describes whether you can delete FULLTEXT indexed columns of different types by executing the ALTER TABLE DDL statement in a MySQL database and a MySQL tenant of OceanBase Database.

Column type in a MySQL database	Deletion allowed	Column type in a MySQL tenant of OceanBase Database	Deletion allowed
CHAR	Yes	CHAR	No
VARCHAR	Yes	VARCHAR	No
TINYTEXT	Yes	TINYTEXT	No
MEDIUMTEXT	Yes	MEDIUMTEXT	No
TEXT	Yes	TEXT	No
LONGTEXT	Yes	LONGTEXT	No
		BINARY	No
		VARBINARY	No
NCHAR	Yes	CHAR	No
JSON	Yes (However, if a column is involved in a functional dependency, the column cannot be deleted.)