Oracle SQL日期比较

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需要to_date函数把常量转换成日期

select * from TBL_STUDENT where LAST_UPDATE_TIME <= to_date('2016-05-30 00:00:00','yyyy-mm-dd hh24:mi:ss')

如果输入库里的时间不是24小时的，是带am,pm的

select * from TBL_STUDENT where LAST_UPDATE_TIME <= to_date('2016-05-30 00:00:00 am','yyyy-mm-dd hh24:mi:ss am')

可能会出现以下错误
ORA-01855:am/a.m or pm/p.m. required

这是因为NLS_DATE_LANGUAGE的设置问题。执行以下语句查看

select * from v$nls_parameters;

PARAMETER VALUE
NLS_LANGUAGE SIMPLIFIED CHINESE
NLS_TERRITORY CHINA
NLS_CURRENCY ￥
NLS_ISO_CURRENCY CHINA
NLS_NUMERIC_CHARACTERS .,
NLS_CALENDAR GREGORIAN
NLS_DATE_FORMAT DD-MON-RR
NLS_DATE_LANGUAGE SIMPLIFIED CHINESE
NLS_CHARACTERSET UTF8
NLS_SORT BINARY
NLS_TIME_FORMAT HH.MI.SSXFF AM
NLS_TIMESTAMP_FORMAT DD-MON-RR HH.MI.SSXFF AM
NLS_TIME_TZ_FORMAT HH.MI.SSXFF AM TZR
NLS_TIMESTAMP_TZ_FORMAT DD-MON-RR HH.MI.SSXFF AM TZR
NLS_DUAL_CURRENCY ￥
NLS_NCHAR_CHARACTERSET UTF8
NLS_COMP BINARY
NLS_LENGTH_SEMANTICS BYTE
NLS_NCHAR_CONV_EXCP FALSE

发现NLS_DATE_LANGUAGE是SIMPLIFIED CHINESE，并不是AMERICAN。所以修改如下

select * from TBL_STUDENT where LAST_UPDATE_TIME <= to_date('2016-05-30 00:00:00 上午','yyyy-mm-dd hh24:mi:ss am')

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