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MODIFY COLUMN | TiDB SQL Statement Reference
An overview of the usage of MODIFY COLUMN for the TiDB database.
/docs/dev/sql-statements/sql-statement-modify-column/
/docs/dev/reference/sql/statements/modify-column/

MODIFY COLUMN

The ALTER TABLE.. MODIFY COLUMN statement modifies a column on an existing table. The modification can include changing the data type and attributes. To rename at the same time, use the CHANGE COLUMN statement instead.

Synopsis

AlterTableStmt:

AlterTableStmt

AlterTableSpec:

AlterTableSpec

ColumnKeywordOpt:

ColumnKeywordOpt

ColumnDef:

ColumnDef

ColumnPosition:

ColumnPosition

Examples

mysql> CREATE TABLE t1 (id int not null primary key AUTO_INCREMENT, col1 INT);
Query OK, 0 rows affected (0.11 sec)

mysql> INSERT INTO t1 (col1) VALUES (1),(2),(3),(4),(5);
Query OK, 5 rows affected (0.02 sec)
Records: 5  Duplicates: 0  Warnings: 0

mysql> ALTER TABLE t1 MODIFY col1 BIGINT;
Query OK, 0 rows affected (0.09 sec)

mysql> SHOW CREATE TABLE t1\G
*************************** 1. row ***************************
       Table: t1
Create Table: CREATE TABLE `t1` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `col1` bigint(20) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin AUTO_INCREMENT=30001
1 row in set (0.00 sec)

MySQL compatibility

  • Does not support modifying multiple columns in a single ALTER TABLE statement. For example:

    ALTER TABLE t1 MODIFY col1 BIGINT, MODIFY id BIGINT NOT NULL;
ERROR 1105 (HY000): Unsupported multi schema change

  • Does not support changes of lossy data types and some other types (including changes from integer to string or to BLOB). For example:

    CREATE TABLE t1 (col1 BIGINT);
ALTER TABLE t1 MODIFY col1 INT;
ERROR 8200 (HY000): Unsupported modify column length 11 is less than origin 20

  • Does not support modifying the precision of the DECIMAL data type. For example:

    CREATE TABLE t (a DECIMAL(5, 3));
ALTER TABLE t MODIFY COLUMN a DECIMAL(6, 3);
ERROR 8200 (HY000): Unsupported modify column: can't change decimal column precision

See also