MODIFY COLUMN

ALTER TABLE .. MODIFY COLUMN 语句用于修改已有表上的列,包括列的数据类型和属性。若要同时重命名,可改用 CHANGE COLUMN 语句。

语法图

AlterTableStmt:

AlterTableStmt

AlterTableSpec:

AlterTableSpec

ColumnKeywordOpt:

ColumnKeywordOpt

ColumnDef:

ColumnDef

ColumnPosition:

ColumnPosition

示例

CREATE TABLE t1 (id int not null primary key AUTO_INCREMENT, col1 INT);
Query OK, 0 rows affected (0.11 sec)
INSERT INTO t1 (col1) VALUES (1),(2),(3),(4),(5);
Query OK, 5 rows affected (0.02 sec)
Records: 5  Duplicates: 0  Warnings: 0
ALTER TABLE t1 MODIFY col1 BIGINT;
Query OK, 0 rows affected (0.09 sec)
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 兼容性

  • 不支持在单个 ALTER TABLE 语句修改多个列,例如:

    ALTER TABLE t1 MODIFY col1 BIGINT, MODIFY id BIGINT NOT NULL;
    ERROR 1105 (HY000): Unsupported multi schema change
    
  • 不支持有损变更,以及部分数据类型的更改(包括整数改为字符串或 BLOB 格式等)。例如:

    CREATE TABLE t1 (col1 BIGINT);
    ALTER TABLE t1 MODIFY col1 INT;
    ERROR 8200 (HY000): Unsupported modify column length 11 is less than origin 20
    
  • 不支持修改 decimal 类型的精度。例如:

    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
    

另请参阅