I am trying to insert data into a SQL table. The data types I am having issues with are nullable floats. When the NULL values are inserted they change to 0. How can I keep them NULL.
private void InsertStatisticsData(DataTable dt)
{
//check isin periodicity and As of Date
foreach(DataRow row in dt.Rows)
{
DataTable queryResultTable = SQL.Query($#"SELECT * FROM Statistics
WHERE [CodeID] = '{row["CodeID"]}'
AND [Periodicity] = '{row["Periodicity"]}'
AND [As of Date] = '{row["As of Date"]}'");
if(queryResultTable.Rows.Count == 0)
{
//Check for Null Values
for(int i = 0; i < row.ItemArray.Count(); i++)
{
if (Convert.ToString(row[i]) == "")
row[i] = (object)DBNull.Value;
}
//Insert Data Into DataBase
SQL.NonQuery($#"INSERT INTO Statistics
VALUES ('{row["CodeID"]}' ,
'{row["Volatility"]}',
'{row["Beta"]}',
'{row["Info Ratio"]}',
'{row["Tracking"]}',
'{row["Drawdown"]}',
'{row["Periodicity"]}',
'{row["As of Date"]}')");
}
}
}
Nonquery Function:
public static void NonQuery(string query, string databaseName = "Database", string serverAddress = "server-name", int commandTimeout = 30)
{
string connString = $"Server = {serverAddress}; Database = {databaseName}; Trusted_Connection = True";
using (SqlConnection sqlConn = new SqlConnection(connString))
using (SqlCommand cmd = new SqlCommand(query, sqlConn))
{
sqlConn.Open();
cmd.CommandTimeout = commandTimeout;
cmd.ExecuteNonQuery();
}
}
You need to make sure your database column structure contains NULL types where you actually need them.
Also make sure you don't have any default constraints set, which automatically values the columns to 0 when null is assigned.
if(Convert.ToString(null) == "")
will be evaluated as false.
so below code won't get executed
row[i] = (object)DBNull.Value;
on a side note, you should use SqlParameters instead of appending values in a string.
This may seem a little heavy handed and bloaty, but if you use parameters (and you really, truly should), I have an extention method I use in my project to take any command object and loop through the parameters to turn a .NET null into a DbNull:
private static void ProcessNullParameters(this DbCommand command)
{
foreach (DbParameter param in command.Parameters)
{
if (param.Value == null)
param.Value = DBNull.Value;
}
}
This way, if your native object returns a null value, you can call the extention method against the command object. I couldn't tell what your SQL object was in your example (a framework of some type?), but presumably, somewhere behind the scenes something like this would be going on:
SqlCommand cmd = new SqlCommand("insert into Statistics values (#Code, #Volatility)", conn);
cmd.Parameters.Add("#Code", SqlDbType.VarChar);
cmd.Parameters.Add("#Volatility", SqlDbType.Decimal);
foreach (DataRow dr in dt.Rows)
{
cmd.Parameters[0].Value = dr["Code"];
cmd.Parameters[1].Value = dr["Volatility"];
// And here you convert your nulls to DbNull
cmd.ProcessNullParameters();
cmd.ExecuteNonQuery();
}
The alternative would be to do this on every value declaration that is nullable.
cmd.Parameters[0].Value = dr["Code"] ?? DbNull.Value
cmd.Parameters[1].Value = dr["Volatility"] ?? DbNull.Value;
I have a database with the infos of the buyers of my product, but I would like it to send the value provided by the program to the database, if it is null, how can I do this?
Code:
I have a database with the infos of the buyers of my product, but I would like it to send the value provided by the program to the database, if it is null, how can I do this?
Code:
string comando = "SELECT COUNT(*) FROM tbl_usuario WHERE user=#Usuario AND pw=#Senha AND tipo=1";
var connection = new MySqlConnection(connString);
var cmd = new MySqlCommand(comando, connection);
cmd.Parameters.AddWithValue("#Usuario", usuario);
cmd.Parameters.AddWithValue("#Senha", senha);
var command = connection.CreateCommand();
connection.Open();
MySqlDataReader leitor = cmd.ExecuteReader();
while (leitor.Read())
{
hd_id = leitor["id"].ToString();
}
if (hd_id == null)
{
//Code i need here
}
int retorno = Convert.ToInt32(cmd.ExecuteScalar());
connection.Close();
There is quite a bit that has been lost in translation in this question, but from I think I am reading I think you want the ID from the database to be retrieved. But the query is just running a count command which will not contain that.
string comando = "SELECT COUNT(*) FROM tbl_usuario WHERE user=#Usuario AND pw=#Senha AND tipo=1";
should actually be
string comando = "SELECT id FROM tbl_usuario WHERE user=#Usuario AND pw=#Senha AND tipo=1";
As you are only returning 1 value (or null if no record match) then you do not need to use a reader; and you can read the return directly, and check for null
var sqlReturn = cmd.ExecuteScalar();
if (sqlReturn == null) { /* Code i need here */ }
else { hd_id = (int)sqlReturn; }
If I did not understand the question; please feel free to let me know and we'll see if we can get you fixed up.
C#
cmd.Parameters.AddWithValue("#Usuario", String.IsNullOrEmpty(usuario) ? DBNull.Value : usuario);
cmd.Parameters.AddWithValue("#Senha", String.IsNullOrEmpty(senha) ? DBNull.Value : senha);
EDIT: I am not able to format my code below, if any one can fix it.
I am new to sql queries and still learning.
Table Name: CommissionSetupTable.
I want to display #Paisa if gross_amount is between the range of #FromRate and #ToRate
Below is my code:
string paisa;
private void load_commission_setup()
{
SqlCeConnection conn = null;
SqlCeCommand cmd = null;
SqlCeDataReader rdr = null;
try
{
conn =
new SqlCeConnection(
#"Data Source=|DataDirectory|\Database.sdf;Persist Security Info=False");
conn.Open();
int rowindex = purchaseBillTableDataGridView.Rows.Count - 1;
gross_amount = double.Parse(purchaseBillTableDataGridView[10, rowindex].Value.ToString());
// Gross Amount is between the ranges of FromRate and ToRate.
cmd = new SqlCeCommand("SELECT Paisa FROM CommissionSetupTable WHERE='" + gross_amount.ToString() + "' BETWEEN #FromRate AND #ToRate;", conn);
rdr = cmd.ExecuteReader();
if (rdr == null)
{
}
else
{
while (rdr.Read())
{
paisa = rdr["Paisa"].ToString();
}
rdr.Close();
cmd.Dispose();
}
}
finally
{
conn.Close();
int rowindex = purchaseBillTableDataGridView.Rows.Count - 1;
purchaseBillTableDataGridView[11, rowindex].Value = paisa;
}
}
The correct syntax to use here is the following
cmd = new SqlCeCommand(#"SELECT Paisa FROM CommissionSetupTable
WHERE #gross BETWEEN FromRate AND ToRate;", conn);
Notice that the two field names should not be prefixed with #, otherwise they will be considered parameters placeholders.
And now, before executing the command, add the parameter for the #gross placeholder
cmd.Parameters.Add("#gross", SqlDbType.Decimal).Value = gross_amount;
I don't know what is the exact datatype of the columns FromRate and EndRate, but
note that you should use the correct datatype for your parameter. Do not pass a string and expect the database engine do the conversion for you. (or worse concatenate your value to the rest of the sql using ToString()). This is always wrong also if sometime the database engine could understand your values.
EDIT
Also, following your comments below, it appears that this line is wrong
int rowindex = purchaseBillTableDataGridView.Rows.Count - 1;
If your DataGridView has the property AllowUserToAddRow set to True then you want to use
int rowindex = purchaseBillTableDataGridView.Rows.Count - 2;
because the first line points to the empty row added to the DataGridView for inserting a new record.
I want to get the value to insert a table in C#,something like this:
begin
insert into bk_library(floor,section) values('foo2','bar')
returning id into :outid;
select *from bk_library where id=:outid;
end;
Unfortunately, I failed
error info: Kiss.Linq.Linq2Sql.Test.EntryPoint.TestInsertReturnId:
Oracle.DataAccess.Client.OracleException : ORA-06550: line 3, column
1: PLS-00428: an INTO clause is expected in this SELECT statement
[Test]
public void TestInsertReturnId()
{
int ret = 0;
string connstring = "Data Source=(DESCRIPTION=(ADDRESS_LIST=(ADDRESS=(PROTOCOL=TCP)(HOST=localhost)(PORT=1521)))(CONNECT_DATA=(SERVER=DEDICATED)(SERVICE_NAME=pdborcl)));User Id=system;Password=****;";
string sql = #"insert into bk_library(floor,section) values('foo','bar') returning id into :outid";
sql = getSqlString();
using (DbConnection conn = new OracleConnection(connstring))
{
conn.Open();
DbCommand command = conn.CreateCommand();
command.CommandType = CommandType.Text;
command.CommandText = sql;
OracleParameter lastId = new OracleParameter(":outid", OracleDbType.Int32);
lastId.Direction = ParameterDirection.Output;
command.Parameters.Add(lastId);
ret = command.ExecuteNonQuery();
// this code work fine ,now I want to get the entire record
LogManager.GetLogger<EntryPoint>().Info("The new id ={0}", lastId.Value.ToString());
conn.Close();
}
Assert.AreNotEqual(ret, 0);
}
ParameterDirection should be ReturnValue
lastId.Direction = ParameterDirection.ReturnValue;
From < http://arjudba.blogspot.ch/2008/07/pls-00428-into-clause-is-expected-in.html?m=1>
You need to write SELECT * INTO some_variable FROM bk_library instead of SELECT * FROM bk_library because I assume you want to store the data retrieved somehow. Therefore you need to declare a new variable some_variable (I assume of type string) and modify your SELECT statement as above. The data from the statement will then be stored in your new variable.
Hope this helps
I am using the following SQL query and the ExecuteScalar() method to fetch data from an Oracle database:
sql = "select username from usermst where userid=2"
string getusername = command.ExecuteScalar();
It is showing me this error message:
System.NullReferenceException: Object reference not set to an instance of an object
This error occurs when there is no row in the database table for userid=2.
How should I handle this situation?
According to MSDN documentation for DbCommand.ExecuteScalar:
If the first column of the first row in the result set is not found, a
null reference (Nothing in Visual Basic) is returned. If the value in
the database is null, the query returns DBNull.Value.
Consider the following snippet:
using (var conn = new OracleConnection(...)) {
conn.Open();
var command = conn.CreateCommand();
command.CommandText = "select username from usermst where userid=2";
string getusername = (string)command.ExecuteScalar();
}
At run-time (tested under ODP.NET but should be the same under any ADO.NET provider), it behaves like this:
If the row does not exist, the result of command.ExecuteScalar() is null, which is then casted to a null string and assigned to getusername.
If the row exists, but has NULL in username (is this even possible in your DB?), the result of command.ExecuteScalar() is DBNull.Value, resulting in an InvalidCastException.
In any case, the NullReferenceException should not be possible, so your problem probably lies elsewhere.
First you should ensure that your command object is not null. Then you should set the CommandText property of the command to your sql query. Finally you should store the return value in an object variable and check if it is null before using it:
command = new OracleCommand(connection)
command.CommandText = sql
object userNameObj = command.ExecuteScalar()
if (userNameObj != null)
string getUserName = userNameObj.ToString()
...
I'm not sure about the VB syntax but you get the idea.
I just used this:
int? ReadTerminalID()
{
int? terminalID = null;
using (FbConnection conn = connManager.CreateFbConnection())
{
conn.Open();
FbCommand fbCommand = conn.CreateCommand();
fbCommand.CommandText = "SPSYNCGETIDTERMINAL";
fbCommand.CommandType = CommandType.StoredProcedure;
object result = fbCommand.ExecuteScalar(); // ExecuteScalar fails on null
if (result.GetType() != typeof(DBNull))
{
terminalID = (int?)result;
}
}
return terminalID;
}
The following line:
string getusername = command.ExecuteScalar();
... will try to implicitly convert the result to string, like below:
string getusername = (string)command.ExecuteScalar();
The regular casting operator will fail if the object is null.
Try using the as-operator, like this:
string getusername = command.ExecuteScalar() as string;
sql = "select username from usermst where userid=2"
var _getusername = command.ExecuteScalar();
if(_getusername != DBNull.Value)
{
getusername = _getusername.ToString();
}
Check out the example below:
using System;
using System.Data;
using System.Data.SqlClient;
class ExecuteScalar
{
public static void Main()
{
SqlConnection mySqlConnection =new SqlConnection("server=(local)\\SQLEXPRESS;database=MyDatabase;Integrated Security=SSPI;");
SqlCommand mySqlCommand = mySqlConnection.CreateCommand();
mySqlCommand.CommandText ="SELECT COUNT(*) FROM Employee";
mySqlConnection.Open();
int returnValue = (int) mySqlCommand.ExecuteScalar();
Console.WriteLine("mySqlCommand.ExecuteScalar() = " + returnValue);
mySqlConnection.Close();
}
}
from this here
SQL NULL value
equivalent in C# is DBNull.Value
if a NULLABLE column has no value, this is what is returned
comparison in SQL: IF ( value IS NULL )
comparison in C#: if (obj == DBNull.Value)
visually represented in C# Quick-Watch as {}
Best practice when reading from a data reader:
var reader = cmd.ExecuteReader();
...
var result = (reader[i] == DBNull.Value ? "" : reader[i].ToString());
In my experience, there are some cases the returned value can be missing and thus execution fails by returning null. An example would be
select MAX(ID) from <table name> where <impossible condition>
The above script cannot find anything to find a MAX in. So it fails. In these such cases we must compare the old fashion way (compare with C# null)
var obj = cmd.ExecuteScalar();
var result = (obj == null ? -1 : Convert.ToInt32(obj));
If you either want the string or an empty string in case something is null, without anything can break:
using (var cmd = new OdbcCommand(cmdText, connection))
{
var result = string.Empty;
var scalar = cmd.ExecuteScalar();
if (scalar != DBNull.Value) // Case where the DB value is null
{
result = Convert.ToString(scalar); // Case where the query doesn't return any rows.
// Note: Convert.ToString() returns an empty string if the object is null.
// It doesn't break, like scalar.ToString() would have.
}
return result;
}
Always have a check before reading row.
if (SqlCommand.ExecuteScalar() == null)
{
}
This is the easiest way to do this...
sql = "select username from usermst where userid=2"
object getusername = command.ExecuteScalar();
if (getusername!=null)
{
//do whatever with the value here
//use getusername.toString() to get the value from the query
}
In your case either the record doesn't exist with the userid=2 or it may contain a null value in first column, because if no value is found for the query result used in SQL command, ExecuteScalar() returns null.
Alternatively, you can use DataTable to check if there's any row:
SqlCommand cmd = new SqlCommand("select username from usermst where userid=2", conn);
SqlDataAdapter adp = new SqlDataAdapter(cmd);
DataTable dt = new DataTable();
adp.Fill(dt);
string getusername = "";
// assuming userid is unique
if (dt.Rows.Count > 0)
getusername = dt.Rows[0]["username"].ToString();
private static string GetUserNameById(string sId, string connStr)
{
System.Data.SqlClient.SqlConnection conn = new System.Data.SqlClient.SqlConnection(connStr);
System.Data.SqlClient.SqlCommand command;
try
{
// To be Assigned with Return value from DB
object getusername;
command = new System.Data.SqlClient.SqlCommand();
command.CommandText = "Select userName from [User] where userid = #userid";
command.Parameters.AddWithValue("#userid", sId);
command.CommandType = CommandType.Text;
conn.Open();
command.Connection = conn;
//Execute
getusername = command.ExecuteScalar();
//check for null due to non existent value in db and return default empty string
string UserName = getusername == null ? string.Empty : getusername.ToString();
return UserName;
}
catch (Exception ex)
{
throw new Exception("Could not get username", ex);
}
finally
{
conn.Close();
}
}
Slight conjecture: if you check the stack for the exception, it is being thrown then the ADO.NET provider for Oracle is reading the underlying rowset to get the first value.
If there is no row, then there is no value to find.
To handle this case execute for a reader and handle Next() returning false for the case of no match.
I Use it Like This with Microsoft Application Block DLL (Its a help library for DAL operations)
public string getCopay(string PatientID)
{
string sqlStr = "select ISNULL(Copay,'') Copay from Test where patient_id=" + PatientID ;
string strCopay = (string)SqlHelper.ExecuteScalar(CommonCS.ConnectionString, CommandType.Text, sqlStr);
if (String.IsNullOrEmpty(strCopay))
return "";
else
return strCopay ;
}
I have seen in VS2010
string getusername = command.ExecuteScalar();
gives compilation error,
Cannot implicitly convert type object to string.
So you need to write
string getusername = command.ExecuteScalar().ToString();
when there is no record found in database it gives error
Object reference not set to an instance of an object
and when I comment '.ToString()', it is not give any error. So I can say ExecuteScalar not throw an exception. I think anserwer given by #Rune Grimstad is right.
I had this issue when the user connecting to the database had CONNECT permissions, but no permissions to read from the database. In my case, I could not even do something like this:
object userNameObj = command.ExecuteScalar()
Putting this in a try/catch (which you should probably be doing anyway) was the only way I could see to handle the insufficient permission issue.
object objUserName;
objUserName = command.ExecuteScalar();
if (objUserName == null) //if record not found ExecuteScalar returns null
{
return "";
}
else
{
if (objUserName == DBNull.Value) //if record found but value in record field is null
{
return "";
}
else
{
string getusername = objUserName.ToString();
return getusername;
}
}
/* Select some int which does not exist */
int x = ((int)(SQL_Cmd.ExecuteScalar() ?? 0));
I used this in my vb code for the return value of a function:
If obj <> Nothing Then
Return obj.ToString()
Else
Return ""
End If
Try this code, it appears to solve your problem.
Dim MaxID As Integer = Convert.ToInt32(IIf(IsDBNull(cmd.ExecuteScalar()), 1, cmd.ExecuteScalar()))
I'm using Oracle.
If your sql returns numeric value, which is int, you need to use Convert.ToInt32(object). Here is the example below:
public int GetUsersCount(int userId)
{
using (var conn = new OracleConnection(...)){
conn.Open();
using(var command = conn.CreateCommand()){
command.CommandText = "select count(*) from users where userid = :userId";
command.AddParameter(":userId", userId);
var rowCount = command.ExecuteScalar();
return rowCount == null ? 0 : Convert.ToInt32(rowCount);
}
}
}
Try this
sql = "select username from usermst where userid=2"
string getusername = Convert.ToString(command.ExecuteScalar());