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
ALTERIgnoreOptionalTABLETableNameAlterTableSpecListOptAlterTablePartitionOptANALYZEPARTITIONPartitionNameListINDEXIndexNameListAnalyzeOptionListOpt
AlterTableSpec
TableOptionListSETTIFLASHREPLICALengthNumLocationLabelListCONVERTTOCharsetKwCharsetNameDEFAULTOptCollateADDColumnKeywordOptIfNotExistsColumnDefColumnPosition(TableElementList)ConstraintPARTITIONIfNotExistsNoWriteToBinLogAliasOptPartitionDefinitionListOptPARTITIONSNUMCHECKTRUNCATEPARTITIONOPTIMIZEREPAIRREBUILDPARTITIONNoWriteToBinLogAliasOptAllOrPartitionNameListCOALESCEPARTITIONNoWriteToBinLogAliasOptNUMDROPColumnKeywordOptIfExistsColumnNameRestrictOrCascadeOptPRIMARYKEYPARTITIONIfExistsPartitionNameListKeyOrIndexIfExistsCHECKIdentifierFOREIGNKEYIfExistsSymbolEXCHANGEPARTITIONIdentifierWITHTABLETableNameWithValidationOptIMPORTDISCARDPARTITIONAllOrPartitionNameListTABLESPACEREORGANIZEPARTITIONNoWriteToBinLogAliasOptReorganizePartitionRuleOptORDERBYAlterOrderItem,DISABLEENABLEKEYSMODIFYColumnKeywordOptIfExistsCHANGEColumnKeywordOptIfExistsColumnNameColumnDefColumnPositionALTERColumnKeywordOptColumnNameSETDEFAULTSignedLiteral(Expression)DROPDEFAULTCHECKIdentifierEnforcedOrNotINDEXIdentifierIndexInvisibleRENAMECOLUMNKeyOrIndexIdentifierTOIdentifierTO=ASTableNameLockClauseAlgorithmClauseFORCEWITHWITHOUTVALIDATIONSECONDARY_LOADSECONDARY_UNLOAD
ColumnKeywordOpt
COLUMN
ColumnDef
ColumnNameTypeSERIALColumnOptionListOpt
ColumnPosition
FIRSTAFTERColumnName

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

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