CHANGE COLUMN
ALTER TABLE.. CHANGE COLUMN 语句用于在已有表上更改列，包括对列进行重命名，和将数据改为兼容类型。
语法图
AlterTableStmt:
AlterTableSpec:
ColumnKeywordOpt:
ColumnName:
ColumnDef:
ColumnPosition:
示例
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>
mysql> ALTER TABLE t1 CHANGE col1 col2 INT;
Query OK, 0 rows affected (0.09 sec)
mysql> ALTER TABLE t1 CHANGE col2 col3 BIGINT, ALGORITHM=INSTANT;
Query OK, 0 rows affected (0.08 sec)
mysql>
mysql> ALTER TABLE t1 CHANGE col3 col3 INT;
ERROR 1105 (HY000): unsupported modify column length 11 is less than origin 20
mysql> ALTER TABLE t1 CHANGE col3 col3 BLOB;
ERROR 1105 (HY000): unsupported modify column type 252 not match origin 8
mysql> ALTER TABLE t1 CHANGE col3 col4 BIGINT, CHANGE id id2 INT NOT NULL;
ERROR 1105 (HY000): can't run multi schema change
MySQL 兼容性
- 目前尚不支持在单个
ALTER TABLE语句中进行多个更改。 - 仅支持特定的数据类型更改。例如，支持将
INTEGER更改为BIGINT，但不支持将BIGINT更改为INTEGER。不支持从整数更改为字符串格式或 BLOB 类型。