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
ALTERIGNORETABLETableNameAddColumnSpec,
TableName
Identifier.Identifier
AddColumnSpec
ADDCOLUMNIF NOT EXISTSColumnNameColumnTypeColumnOptionFIRSTAFTERColumnName
ColumnType
NumericTypeStringTypeDateAndTimeTypeSERIAL
ColumnOption
NOTNULLAUTO_INCREMENTPRIMARYKEYCLUSTEREDNONCLUSTEREDGLOBALLOCALUNIQUEKEYGLOBALLOCALDEFAULTNowSymOptionFractionSignedLiteralNextValueForSequenceSERIALDEFAULTVALUEONUPDATENowSymOptionFractionCOMMENTstringLitCONSTRAINTIdentifierCHECK(Expression)NOTENFORCEDNULLGENERATEDALWAYSAS(Expression)VIRTUALSTOREDREFERENCESTableName(IndexPartSpecificationList)MatchOnDeleteUpdateOptCOLLATECollationNameCOLUMN_FORMATColumnFormatSTORAGEStorageMediaAUTO_RANDOM(LengthNum)

示例

CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY AUTO_INCREMENT);
Query OK, 0 rows affected (0.11 sec)
INSERT INTO t1 VALUES (NULL);
Query OK, 1 row affected (0.02 sec)
SELECT * FROM t1;
+----+ | id | +----+ | 1 | +----+ 1 row in set (0.00 sec)
ALTER TABLE t1 ADD COLUMN c1 INT NOT NULL;
Query OK, 0 rows affected (0.28 sec)
SELECT * FROM t1;
+----+----+ | id | c1 | +----+----+ | 1 | 0 | +----+----+ 1 row in set (0.00 sec)
ALTER TABLE t1 ADD c2 INT NOT NULL AFTER c1;
Query OK, 0 rows affected (0.28 sec)
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 KEYUNIQUE INDEX 设置为 GLOBAL 来设置全局索引。该扩展与 MySQL 不兼容。

另请参阅

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