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ADD COLUMN

ALTER TABLE.. ADD COLUMN 语句在现有表中添加一列。在 TiDB 中,此操作是在线的,意味着添加列不会阻塞对表的读取或写入。

概要

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

mysql> CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY AUTO_INCREMENT); Query OK, 0 rows affected (0.11 sec) mysql> INSERT INTO t1 VALUES (NULL); Query OK, 1 row affected (0.02 sec) mysql> SELECT * FROM t1; +----+ | id | +----+ | 1 | +----+ 1 row in set (0.00 sec) mysql> ALTER TABLE t1 ADD COLUMN c1 INT NOT NULL; Query OK, 0 rows affected (0.28 sec) mysql> SELECT * FROM t1; +----+----+ | id | c1 | +----+----+ | 1 | 0 | +----+----+ 1 row in set (0.00 sec) mysql> ALTER TABLE t1 ADD c2 INT NOT NULL AFTER c1; Query OK, 0 rows affected (0.28 sec) mysql> 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置为 PRIMARY KEY
  • 不支持将新添加的列设置为 AUTO_INCREMENT
  • 对生成列的添加有限制,详见:generated column limitations
  • 在添加新列时,通过指定 PRIMARY KEYUNIQUE INDEXGLOBAL 来设置 global index,这是 TiDB 对 partitioned tables 的扩展,不兼容 MySQL。

相关链接

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