null值从数据库返回如何在asp.net vb中处理它 [英] null value return from database how to handle it in asp.net vb
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问题描述
我在这里使用这样的代码
Dim qry = 从tbl_deal中选择max(ID),其中officeid ='& ddl1.SelectedValue.Trim& '
dun cmd1 as sqlCommand = New SqlCommand(qry,conn)
conn.open()
dim read As SqlDataReader = cmd1.ExecuteReader()
read.Read()
Dim a = 0
if (read.HasValue)然后
a = read( 0 )
endif
a = a + 1
但此代码在nullvalue中给出错误1.谢谢
问候,
Umesh Daiya
解决方案
请使用以下查询:
选择 COALESCE (max(ID), 0 )来自 tbl_deal 其中 officeid = @ officeid
用DbNull
解决你的问题。
给convert.tostring回覆ad(0)如果它的null然后是0并且如果它不为null那么你的函数a = a + 1并且如果不为null则将读取转换为int ............ convert.tostring也可以处理null值它不会抛出错误
如果 不读取( 0 )= DBNull.Value 然后
a =读取( 0 )
end if
Here i use code like this
Dim qry="select max(ID) from tbl_deal where officeid='" & ddl1.SelectedValue.Trim & "'"
dun cmd1 as sqlCommand=New SqlCommand(qry,conn)
conn.open()
dim read As SqlDataReader=cmd1.ExecuteReader()
read.Read()
Dim a=0
if(read.HasValue) Then
a=read(0)
endif
a=a+1
but this code given error in nullvalue its not 1.Thanks
Regards,
Umesh Daiya
解决方案
Please, use below query:
select COALESCE(max(ID),0) from tbl_deal where officeid=@officeid
That resolves your problem withDbNull
.
give convert.tostring to read(0) if its null then 0 and if its not null then your function a=a+1 and convert read to int if not null ............ convert.tostring can handle null values also it will not throw error
If not read(0)= DBNull.Value Then a=read(0) end if
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