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title summary aliases
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' IgnoreOptional 'TABLE' TableName ( AlterTableSpecListOpt AlterTablePartitionOpt | 'ANALYZE' 'PARTITION' PartitionNameList ( 'INDEX' IndexNameList )? AnalyzeOptionListOpt )

AlterTableSpec ::=
    TableOptionList
|   'SET' 'TIFLASH' 'REPLICA' LengthNum LocationLabelList
|   'CONVERT' 'TO' CharsetKw ( CharsetName | 'DEFAULT' ) OptCollate
|   'ADD' ( ColumnKeywordOpt IfNotExists ( ColumnDef ColumnPosition | '(' TableElementList ')' ) | Constraint | 'PARTITION' IfNotExists NoWriteToBinLogAliasOpt ( PartitionDefinitionListOpt | 'PARTITIONS' NUM ) )
|   ( ( 'CHECK' | 'TRUNCATE' ) 'PARTITION' | ( 'OPTIMIZE' | 'REPAIR' | 'REBUILD' ) 'PARTITION' NoWriteToBinLogAliasOpt ) AllOrPartitionNameList
|   'COALESCE' 'PARTITION' NoWriteToBinLogAliasOpt NUM
|   'DROP' ( ColumnKeywordOpt IfExists ColumnName RestrictOrCascadeOpt | 'PRIMARY' 'KEY' | 'PARTITION' IfExists PartitionNameList | ( KeyOrIndex IfExists | 'CHECK' ) Identifier | 'FOREIGN' 'KEY' IfExists Symbol )
|   'EXCHANGE' 'PARTITION' Identifier 'WITH' 'TABLE' TableName WithValidationOpt
|   ( 'IMPORT' | 'DISCARD' ) ( 'PARTITION' AllOrPartitionNameList )? 'TABLESPACE'
|   'REORGANIZE' 'PARTITION' NoWriteToBinLogAliasOpt ReorganizePartitionRuleOpt
|   'ORDER' 'BY' AlterOrderItem ( ',' AlterOrderItem )*
|   ( 'DISABLE' | 'ENABLE' ) 'KEYS'
|   ( 'MODIFY' ColumnKeywordOpt IfExists | 'CHANGE' ColumnKeywordOpt IfExists ColumnName ) ColumnDef ColumnPosition
|   'ALTER' ( ColumnKeywordOpt ColumnName ( 'SET' 'DEFAULT' ( SignedLiteral | '(' Expression ')' ) | 'DROP' 'DEFAULT' ) | 'CHECK' Identifier EnforcedOrNot | 'INDEX' Identifier IndexInvisible )
|   'RENAME' ( ( 'COLUMN' | KeyOrIndex ) Identifier 'TO' Identifier | ( 'TO' | '='? | 'AS' ) TableName )
|   LockClause
|   AlgorithmClause
|   'FORCE'
|   ( 'WITH' | 'WITHOUT' ) 'VALIDATION'
|   'SECONDARY_LOAD'
|   'SECONDARY_UNLOAD'

ColumnDef ::=
    ColumnName ( Type | 'SERIAL' ) ColumnOptionListOpt

ColumnPosition ::=
    ( 'FIRST' | 'AFTER' ColumnName )?

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

  • 不支持在一条语句中同时添加多列。
  • 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。

另请参阅