Must declare the scalar variable …
“Must declare the scalar variable …”
Every now and then this error is reported when using parameters in SQL statements.
The two most common reasons for this are:
.1 The parameter is simply misspelled. It is common that when there are many parameters in the parameter list that a misspelled parameter has been missed.
So, for example, running this:
using (SqlConnection con = new SqlConnection(cs))
{
con.Open();
SqlCommand cmd = con.CreateCommand();
cmd.CommandText = "SELECT * FROM Categories WHERE CategoryID = @catId";
cmd.Parameters.Add("@catIdd", System.Data.SqlDbType.Int).Value = 1;
SqlDataReader rdr = cmd.ExecuteReader();
while (rdr.Read())
{
Console.WriteLine("{0} {1}", rdr[0].ToString(), rdr[1].ToString());
}
con.Close();
}
will cause the following exception to be thrown (since the provided parameter name (@catIdd) is misspelled, i.e. not matching the one in the SQL):
System.Data.SqlClient.SqlException: Must declare the scalar variable "@catId".
at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection)
at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj)
...
.2 OleDb classes (OleDbConnection/OleDbCommand etc.) are used. When using OleDb the parameters in the SQL are to be set to ? and not @paramname.
So, for example, running this:
using (OleDbConnection con = new OleDbConnection(cs))
{
con.Open();
OleDbCommand cmd = con.CreateCommand();
cmd.CommandText = "SELECT * FROM Categories WHERE CategoryID = @catId";
cmd.Parameters.Add("@catId", OleDbType.Integer).Value = 1;
OleDbDataReader rdr = cmd.ExecuteReader();
while (rdr.Read())
{
Console.WriteLine("{0} {1}", rdr[0].ToString(), rdr[1].ToString());
}
con.Close();
}
will cause the following exception to be thrown since the provided parameter name in the SQL String (@catId) is wrong. Replace it with ? (… WHERE CategoryID = ?) and it should be fine.
System.Data.OleDb.OleDbException: Must declare the scalar variable "@catId".
at System.Data.OleDb.OleDbDataReader.ProcessResults(OleDbHResult hr)
at System.Data.OleDb.OleDbDataReader.NextResult()
...