问题
i am trying to execute the records that have TotalTime null value from the table NewTimeAttendance...TotalTime datatype nchar(10)
select * from newtimeattendance where TotalTime = 'NULL'
....nothing
select * from newtimeattendance where TotalTime = 'null'
....nothing
select * from newtimeattendance where TotalTime = 'Null'
....nothing
select * from newtimeattendance where TotalTime = null
....nothing
select * from newtimeattendance where TotalTime = Null
....nothing
select * from newtimeattendance where TotalTime = NULL
....nothing
when i select the whole table i can see that there is some NULL TotalTime values..!!
it is small select statment ..why doesn't it work ? is there a way (special way ) to execute the 'NULL' with nchar type ?!
thanks in advance
回答1:
You need to use IS NULL
select * from newtimeattendance where TotalTime IS NULL
The MySQL doc has some good information on dealing with NULL values: http://dev.mysql.com/doc/refman/5.0/en/working-with-null.html
来源：https://stackoverflow.com/questions/2452783/executing-null-values-records