update statement in c#

Question

Anyone knows why tihs code doesn't work? Program says "Invalid use of null". In access thise code is working, but not hire. UPDATE cas SET cas.skupaj = CDbl([Odhod]-[Prihod])*24;

try
{
    OleDbConnection conn = GetConnection();
    conn.Open();

    String MyString = @"UPDATE cas SET skupaj = CDbl(Odhod-Prihod)*24 " ;  

    OleDbCommand command = new OleDbCommand(MyString, conn);
    command.ExecuteNonQuery();
    conn.Close();
    MessageBox.Show("Uspešno dodano v PB!");
}
catch (Exception ex)
{
    MessageBox.Show(ex.Message);
}

This is really confusing. The error message Invalid use of null is an Access error message. How are you getting that in C# code? When you say this works in access, that means you can run that exact SQL statement above in Access without any errors? — mellamokb
– mellamokb, Commented Apr 11, 2013 at 20:07
Might be due to NULL value for any one of column (Odhod-Prihod), AS CDate cannot handle Null values. — Vijaysing Gusinge
– Vijaysing Gusinge, Commented Apr 11, 2013 at 20:09
Code that HansUp posted it is working. In querry must be where is Odhod Not Null and Prihod Not Null. — CrashDown
– CrashDown, Commented Apr 11, 2013 at 20:26

HansUp · Accepted Answer · 2013-04-11 20:13:10Z

5

In an Access Immediate window session, these statements throw error 94, "Invalid use of Null".

? CDbl(Null)
? CDbl(10 - Null)
? CDbl(Null - 10)
? CDbl(Null - Null)

Revise your query to make sure you don't give CDbl() Null values.

UPDATE cas
SET skupaj = CDbl(Odhod-Prihod)*24
WHERE
        Odhod Is Not Null
    AND Prihod Is Not Null

OTOH, it's not clear why you need to store that calculated value to skupaj. You could use a SELECT query to return it whenever you need, and that way you wouldn't have to run the UPDATE again whenever Odhod or Prihod values change.

SELECT CDbl(Odhod-Prihod)*24 AS skupaj
FROM cas
WHERE
        Odhod Is Not Null
    AND Prihod Is Not Null

edited Apr 11, 2013 at 20:13

answered Apr 11, 2013 at 20:07

HansUp

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