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How do I insert NULL values in a SQL database using C#.net

Posted on 2008-10-20
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Last Modified: 2011-10-03
I have an insert statement that looks like this.

Insert into databasTable (col1,col2,col3) values(id + '" + callBackTime + "','" + reqCallDuration + "','" )

I accept input from 3 differet text boxes then assign the value to the string variables id/callbackTime/reqCallDuration

I need to insert a null value in for example col3- reqCallDuration if that text box was not filled.

How do I do this?

the col3 accepts null values in the database
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Question by:wademi
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6 Comments
 
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Expert Comment

by:Wikkard
ID: 22763495
Use dbnull.value this represents a database null.
So check if the text boxes are empty then pass dbnull.value instead of an empty string.
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LVL 8

Expert Comment

by:Wikkard
ID: 22763526
The use of  DBNull.value only really applies if you are using parametised queries (or stored procs).
If you are creating inline sql strings (which I think you are based on your question) you can simply put the text NULL into your inline sql string.

ie.
id =1;
callbackTime = "2008-12-24 23:59:59";
reqcallDuration = "NULL"
string strsql = "insert into databaseTable(col1, col2,col3) value (" + id + ", " + callbackTime + ", " +  reqcallDuration + ")";

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Author Comment

by:wademi
ID: 22764194
I tried reqcallDuration = "NULL" before.
if I look at the table in the database the field will be NULL.
When I display the NULL field in a label in my application ithe label actually displays "NULL".

I believe the label blank when displayed if the value is NULL
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Accepted Solution

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Wikkard earned 1500 total points
ID: 22765935
How are you inserting records ?
Are you using a command object  to run SQL commands on the database or using a dataadapter configured with the appropriate insert command ?

It sounds like you are using an insert command which when configured via the designer/wizard will create a parametized query. In this case you need to set the value to DBNull.Value.

Depends on how the label is populated as to whether it will display null or an empty string. Could you provide more info on how the label is populated? Is this an ASP.NET or winforms application ?


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Expert Comment

by:norton127
ID: 23621592
using dbnull.value while in parameterized query is suggestable. U have to use parameterized queries for the security purpose.inserting of datadirectly by using text boxes ( First i used them) is not suggestable.
go for parameterized query
I am giving Code  for you.
dim cmd as new sqlcommand(insert into tablename (col1,col2,col3) values (@col1,@col2,@col3),connection)
 cmd.Parameters.Add(New SqlParameter("@col1", SqlDbType.NVarChar, 255))
 cmd.Parameters.Add(New SqlParameter("@col2", SqlDbType.NVarChar, 255))
 cmd.Parameters.Add(New SqlParameter("@col3", SqlDbType.NVarChar, 255))
cmd.Parameters("@col1").Value = txtbox.Text
cmd.Parameters("@col2").Value = dbnull.value
 
or 
 
if txtbox1.text="" then 
cmd.Parameters("@col2").Value = dbnull.value
else
cmd.Parameters("@col2").Value = textbox1.text
end if 
 
cmd.Parameters("@col3").Value = txttbox3.Text
 
connection.open
cmd.executenonquery
connection.close
end sub

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Expert Comment

by:norton127
ID: 23621601
While i am inserting Textbox1.text="NULL" it is taking string NULL into database and it will give string value null for your label not null value.
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