下列与修改表结构相关的命令是()。 A.INSERT B.ALTERC.UPDATED.CR
问题详情
下列与修改表结构相关的命令是()。
A.INSERT
B.ALTER
C.UPDATE
D.CREATE请帮忙给出正确答案和分析，谢谢！
参考答案
正确答案：B
B。【解析】修改表结构的命令是ALTERTABLE，该命令有3种格式：①ALTERTABLETableNamelADDIALTER[COL一UMN]FieldNamelFieldTyper(nFieldWidth[nPrecismn])][NULLINOTNULL][CHECKlExpressionl[ERRORcMessageTextL1][DEFAULTeExpressionl][PRIMARYKEYKEYUNIQUE][REFERENC：EsTableName2[TA(TAGTagName]]②ALTERTABLETableNamelALTER[COLUMN]FieldName2[NULL1NOTNULL][SETDELAULTeExpression2][SETCHECKlExpression2[ERRRcMessageText2][DROPDEFAUl，T][DR1’CHECK]③ALTERTABLETableNamel[DROP[COLIJMN]FieldName3][SETCHECKlExpression3[ERRORcMessageText3]][DROPCHECK][[ADDPRIMARYKEYeExpression3TAGTagName2[FOR1Expression4]][DROPPRIMARYKEY)[ADDUNIQUEeExpression4[TAGTagName3[FOR1ExpressionS]]][DROPUNIQUETAGTagName4][ADDFOREIGNKEY[eExpression5]TAGTagName4[FORlExpression6]REFERENCESTableName2[TAGTagName5]][DROPFOREIGNKEYTAGTagName6[sAVE]][RENAMEcOLUMNFieldName4TOFieldName5]
