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ADD COLUMN
TiDB 数据库中 ADD COLUMN 的使用概况。
/docs-cn/dev/sql-statements/sql-statement-add-column/
/docs-cn/dev/reference/sql/statements/add-column/

ADD COLUMN

ALTER TABLE.. ADD COLUMN 语句用于在已有表中添加列。在 TiDB 中，ADD COLUMN 为在线操作，不会阻塞表中的数据读写。

语法图

AlterTableStmt
         ::= 'ALTER' 'IGNORE'? 'TABLE' TableName AddColumnSpec ( ',' AddColumnSpec )*

TableName ::=
    Identifier ('.' Identifier)?

AddColumnSpec
         ::= 'ADD' 'COLUMN' 'IF NOT EXISTS'? ColumnName ColumnType ColumnOption+ ( 'FIRST' | 'AFTER' ColumnName )?

ColumnType
         ::= NumericType
           | StringType
           | DateAndTimeType
           | 'SERIAL'

ColumnOption
         ::= 'NOT'? 'NULL'
           | 'AUTO_INCREMENT'
           | 'PRIMARY'? 'KEY' ( 'CLUSTERED' | 'NONCLUSTERED' )? ( 'GLOBAL' | 'LOCAL' )?
           | 'UNIQUE' 'KEY'? ( 'GLOBAL' | 'LOCAL' )?
           | 'DEFAULT' ( NowSymOptionFraction | SignedLiteral | NextValueForSequence )
           | 'SERIAL' 'DEFAULT' 'VALUE'
           | 'ON' 'UPDATE' NowSymOptionFraction
           | 'COMMENT' stringLit
           | ( 'CONSTRAINT' Identifier? )? 'CHECK' '(' Expression ')' ( 'NOT'? ( 'ENFORCED' | 'NULL' ) )?
           | 'GENERATED' 'ALWAYS' 'AS' '(' Expression ')' ( 'VIRTUAL' | 'STORED' )?
           | 'REFERENCES' TableName ( '(' IndexPartSpecificationList ')' )? Match? OnDeleteUpdateOpt
           | 'COLLATE' CollationName
           | 'COLUMN_FORMAT' ColumnFormat
           | 'STORAGE' StorageMedia
           | 'AUTO_RANDOM' ( '(' LengthNum ')' )?

示例

{{< copyable "sql" >}}

CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY AUTO_INCREMENT);
Query OK, 0 rows affected (0.11 sec)

{{< copyable "sql" >}}

INSERT INTO t1 VALUES (NULL);
Query OK, 1 row affected (0.02 sec)

{{< copyable "sql" >}}

SELECT * FROM t1;
+----+
| id |
+----+
|  1 |
+----+
1 row in set (0.00 sec)

{{< copyable "sql" >}}

ALTER TABLE t1 ADD COLUMN c1 INT NOT NULL;
Query OK, 0 rows affected (0.28 sec)

{{< copyable "sql" >}}

SELECT * FROM t1;
+----+----+
| id | c1 |
+----+----+
|  1 |  0 |
+----+----+
1 row in set (0.00 sec)

{{< copyable "sql" >}}

ALTER TABLE t1 ADD c2 INT NOT NULL AFTER c1;
Query OK, 0 rows affected (0.28 sec)

{{< copyable "sql" >}}

SELECT * FROM t1;
+----+----+----+
| id | c1 | c2 |
+----+----+----+
|  1 |  0 |  0 |
+----+----+----+
1 row in set (0.00 sec)

MySQL 兼容性

  • 不支持将新添加的列设为 PRIMARY KEY。
  • 不支持将新添加的列设为 AUTO_INCREMENT。
  • 对添加生成列有局限性，具体可参考：生成列局限性。
  • TiDB 对分区表进行了扩展，你可以在添加新列时通过将 PRIMARY KEY 或 UNIQUE INDEX 设置为 GLOBAL 来设置全局索引。该扩展与 MySQL 不兼容。

另请参阅