Develop Reference

SQL command string is it okay to concatenate it?

I've been creating a class for buttons where you can add and delete rows from the table's database but it is my first time concatenate a string I have a suspicion that it is not working due to commandtext.
public static void deleteButton(string databaseName, string IDname, DataGridView dgv)
{
Helper.openConnection();
SqlCommand cmd = new SqlCommand();
cmd.Connection = Helper.cn;
string IDLocation = dgv.SelectedRows[0].Cells[0].Value.ToString();
cmd.CommandText = "delete from " + databaseName + " where " + IDname + " = " + IDLocation;
Helper.cn.Close();
MessageBox.Show("Successfully Deleted!");
}
public static void addButton(string databaseName, List<string> values, DataGridView dgv, bool isAdd)
{
Helper.openConnection();
SqlCommand cmd = new SqlCommand();
cmd.Connection = Helper.cn;
string message = isAdd == true? "Sucessfully Added" : "Sucessfully Edited";
string command = "insert into " + databaseName + " values(";
for (int i = 0; i < values.Count; i++)
{
command += values[i];
if(i != values.Count - 1) command += ", ";
}
command += ")";
cmd.CommandText = command;
MessageBox.Show(message);
Helper.cn.Close();
}
thank you for your time helping me.

Two problems:
You're using INSERT INTO [databaseName]. That should be INSERT INTO [tableName]. That's why it's not working.
Don't concatenate values into the SQL text. It opens the door for SQL injection, and it also makes it harder for the SQL server to reuse query plans. Instead, use query parameters. There is an example in the documentation.

I'll leave the design up to you and just attempt to answer the question. Have you actually looked at the command text? Have you tried to paste the command text into a query and run it manually? You need to quote string values. Also your functions and query use 'databaseName'. This should be a table name not a database name.

The commentary here is all on target, but that aside the key issue with your code is you are not doing anything. You have opened the connection, declared the SQL command, but then you don't execute it.
So yes, use parameters, but if you want your SQL to work you need to execute it:
string IDLocation = dgv.SelectedRows[0].Cells[0].Value.ToString();
cmd.CommandText = string.Format("delete from {0} where IDname = #ID", databaseName);
cmd.Parameters.AddWithValue("#ID", IDLocation);
Note you don't need quotes or anything when you use parameters, even on a non-numeric datatype.
And the feature of the evening, the missing link:
cmd.ExecuteNonQuery();
Same goes for your insert query -- be sure to run the execute method, and USE PARAMETERS!

No value given for one or more required parameters error while deleting in database

Every time I execute a DELETE query on my database, the following error results:
No value given for one or more required parameters
I check the names but still have the error. Below is the code used to execute the query:
connection.Open();
OleDbCommand command = new OleDbCommand();
command.Connection = connection;
string query = "delete FROM Accounts WHERE Id_No = " + IdNoBox.Text + "";
command.CommandText = query;
command.ExecuteNonQuery();
MessageBox.Show("Successfully Deleted");
this.Close();
connection.Close();

Assuming Id_No to be string, it should be enclosed in single quotes.Otherwise, it will be considered as a parameter.
the query should string query = "delete FROM Accounts WHERE Id_No = "'" + IdNoBox.Text + "'";

To address the specific question being asked, if Id_No is a character based, there should be single quotes around it. For readability, consider the following syntax.
string query = string.Format("delete FROM Accounts WHERE Id_No = '{0}' ", IdNoBox.Text);
Also note that the connection/command should be disposed of properly, including the cases where an exception occurs. An easy way to do this is with the using clause. See below.
using (var connection = new OleDbConnection())
using (var command = new OleDbCommand(){Connection = connection,CommandText = query})
{
connection.Open();
command.ExecuteNonQuery();
}
MessageBox.Show("Successfully Deleted");

execute sql command in asp.net

I have a problem with executing a sql command to the DB. The command should add a new user to the 'users' table.
But when I run the code, I get this Exception on:
command.ExecuteNonQuery();
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.Data.OleDb.OleDbException: Syntax error in INSERT INTO statement.
this is the code of the page - GetSignIn.cshtml :
#{
string Uname = Request["name"];
string userName = Request["userName"];
string pass = Request["passWord"];
string pic = Request["pic"];
string privacy = Request["privacy"];
if(pic == null)
{
pic = "Shared/defaultPic.jpg";
}
System.Data.OleDb.OleDbConnection connection = new System.Data.OleDb.OleDbConnection();
connection.ConnectionString = #"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\Users\Etay\Documents\Visual Studio 2012\WebSites\Josef\Shared\users.mdb";
try
{
System.Data.OleDb.OleDbCommand command = new System.Data.OleDb.OleDbCommand();
command.Connection = connection;
connection.Open();
command.CommandText = "INSERT INTO users (userName,passWord,Uname,pic) VALUES ('" + userName + "', '" + pass + "', '" + Uname + "', '" + pass + "', " + pic + ")";
command.ExecuteNonQuery();
Response.Redirect("../HtmlPage.html");
}
finally
{
connection.Close();
}
}
What should I change in my code? Why is it happening? Where is the syntax error in the INSERT INTO?

Use parameterized queries. Here is your statement rewritten to make use of them.
I replaced your try/finally with a using block although your try/finally was acceptable.
Parameterized queries prevent errors and Sql Injection Attacks. An error could occur in your existing code if I were to submit a tick as a part of my user name or password. In the current form this would result in an exception. This is because the tick character is used to quote strings in sql syntax.
using (System.Data.OleDb.OleDbConnection connection = new System.Data.OleDb.OleDbConnection())
{
connection.ConnectionString = #"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\Users\Etay\Documents\Visual Studio 2012\WebSites\Josef\Shared\users.mdb";
using (System.Data.OleDb.OleDbCommand command = new System.Data.OleDb.OleDbCommand())
{
command.Connection = connection;
command.CommandText = "INSERT INTO users (userName,passWord,Uname,pic) VALUES (?,?,?,?)";
command.Parameters.Add(userName);
command.Parameters.Add(pass);
command.Parameters.Add(Uname);
command.Parameters.Add(pic);
connection.Open();
command.ExecuteNonQuery();
}
}
About parameters for an OleDb connection from OleDbCommand.Parameters
Remarks
The OLE DB .NET Provider does not support named parameters for passing parameters to an SQL statement or a stored procedure called by an OleDbCommand when CommandType is set to Text. In this case, the question mark (?) placeholder must be used. For example:
SELECT * FROM Customers WHERE CustomerID = ?
Therefore, the order in which OleDbParameter objects are added to the OleDbParameterCollection must directly correspond to the position of the question mark placeholder for the parameter in the command text.

What should I change in my code?
Change to parameters (that also fixes the problem that you don;t have quotes around the pic value)
Remove the second instance of pass in your values
command.CommandText = "INSERT INTO users (userName,passWord,Uname,pic) VALUES (#userName, #pass, #Uname, #pic)";
command.Parameters.Add("#userName").Value = userName;
.. etc.
It's unclear what the type if pic is - you are passing a string but I can;t tell of the column stores a file path or if you are indending to serialize the file and store it in a pinary field.

You set 4 fields after the "INTO" clause, however you're passing 5 parameters:
"INSERT INTO users (userName,passWord,Uname,pic) VALUES ('" + userName + "', '" + pass + "', '" + Uname + "', '" + pass + "', " + pic + ")";
Just add the fifth field, or remove one parameter from the VALUES part

Please check take a look at your Insert statement, it looks like that you provided password value twice.
The number of query values and the destination fields should be same in an INSERT statement.

You have the wrong number parameters in your insert statement. For clarity, why not use string.Format to keep everything uniform? (Assuming these are all string types)
var rawSql = #"Insert INTO Users (userName,passWord,Uname,pic) VALUES ('{0}','{1}','{2}','{3}')";
command.CommandText = string.Format(rawSql, userName, pass, Uname, pic);
command.ExecuteNonQuery();
However, it also looks like you probably want to include that 5th parameter as well - just extend the format :
var rawSql = #"Insert INTO Users (userName,passWord,Uname,pic, privacy) VALUES ('{0}','{1}','{2}','{3}','{4}')";
command.CommandText = string.Format(rawSql, userName, pass, Uname, pic, privacy);
command.ExecuteNonQuery();

Since most of the answers failed to address the SQL Injection vulnerability, here's an example with parameterized queries. In addition to preventing SQL Injection attacks, it also makes it easier to troubleshoot these types of issues, and you don't need to worry about quoting or not quoting parameters.
System.Data.OleDb.OleDbConnection connection = new System.Data.OleDb.OleDbConnection();
connection.ConnectionString = #"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\Users\Etay\Documents\Visual Studio 2012\WebSites\Josef\Shared\users.mdb";
try
{
System.Data.OleDb.OleDbCommand command = new System.Data.OleDb.OleDbCommand();
command.Connection = connection;
connection.Open();
command.CommandText = "INSERT INTO users (userName, passWord, Uname, pic, privacy) VALUES (?, ?, ?, ?, ?)";
command.Parameters.Add(userName);
command.Parameters.Add(pass);
command.Parameters.Add(name);
command.Parameters.Add(pic);
command.Parameters.Add(privacy);
command.ExecuteNonQuery();
Response.Redirect("../HtmlPage.html");
}
finally
{
connection.Close();
}

Tnx 4 the help
It happend to be a problem with the database - you can not apply a INSERT INTO statement where the column name is "password". "password" is a Reserved word
in SQL.
Tnx again,
Etay

Use Variable In SQL String

How can I add a variable to my SQL string and run it against the server successfully? I want to run this statement through my C#
protected void RunSQLQuery(string salesman, string connectionString)
{
SqlConnection cnn;
SqlCommand cmd;
StringBuilder sql = new StringBuilder();
SqlDataReader reader;
cnn = new SqlConnection(connectionString);
sql = new StringBuilder();
sql.Append("update database ");
sql.Append("set shippdate = GetDate() ");
sql.Append("where salesman = "' + salesman + "'");
sql.Append("and managerapproval is not null ");
cnn.Open();
cmd = new SqlCommand(sql.ToString(), cnn);
reader = cmd.ExecuteReader();
reader.Close();
cmd.Dispose();
cnn.Close
}
This presents multiple compile errors underlining my +salesman+ code. The errors are:
Only assignment, call, increment, decrement, and new object
expressions can be used as a statement
; expected
) expected
Too many characters in character literal Newline in constant

You are not adding the string object that salesman refers, you are adding salesman as a string literal.
Just add it as a parameter like;
var cmd = new SqlCommand("update database set shippdate = GetDate() where salesman = #salesman");
cmd.Parameters.Add("#salesman", salesman);
...
And use ExecuteNonQuery to execute your command, not SqlDataReader. This SqlDataReader is for return some data.
But more important, you should always use parameterized queries. This kind of string concatenations are open for SQL Injection attacks.
Also use using statement to dispose your connection and command automatically instead of calling Close or Dispose methods manually.
As a full example;
protected void RunSQLQuery(string salesman, string connectionString)
{
using(var cnn = new SqlConnection(connectionString))
using(var cmd = cnn.CreateCommand())
{
cmd.CommandText = #"update database set shippdate = GetDate()
where salesman = #salesman";
// I assume your column is nvarchar
cmd.Parameters.Add("#salesman", SqlDbType.NVarChar).Value = salesman;
cnn.Open();
cmd.ExecuteNonQuery();
}
}
For myself, I always prefer to use SqlParameterCollection.Add(string, SqlDbType, Int32) overload to specify my parameter type and it's size but since you never mentioned your salesman column type, I couldn't post this in my example.

As you can also see from the syntax highlighting, the compile errors are caused because you did not escape the quotes properly in sql.Append("where salesman = "' + salesman + "'");.
As a side note, you should never insert strings into sql queries without first validating them, or you are open to sql injection, e.g. if i pass "''; drop table database;" as salesman parameter. It is better to use SqlParameter.

I would suggest using the AddWithValue method from your sql command combined with the UPPER function to make it case insensitive:
SqlCommand cmd = cnn.CreateCommand();
cmd.CommandText = "UPDATE database SET shippdate = GetDate() WHERE UPPER(salesman) = UPPER(#salesMan)";
cmd.Parameters.AddWithValue("#salesMan", salesman);
if (cnn.State.Equals(ConnectionState.Closed))
{
cnn.Open();
}
cmd.ExecuteNonQuery();
cnn.Close();

As mentioned in above answers, yes, writing queries in this way is not a good way to do it. But still if you want to do it that way only, you will have to change:
sql.Append("where salesman = "' + salesman + "'");
to
sql.Append("where salesman = '" + salesman + "'");

how to update a table using oledb parameters?

I am having a table which has three fields, namely LM_code,M_Name,Desc. LC_code is a autogenerated string Id, keeping this i am updating M_Name and Desc. I used normal update command, the value is passing in runtime but the fields are not getting updated. I hope using oledb parameters the fields can be updated.
Here is my code.
public void Modify()
{
String query = "Update Master_Accounts set (M_Name='" + M_Name + "',Desc='" + Desc + "') where LM_code='" + LM_code + "'";
DataManager.RunExecuteNonQuery(ConnectionString.Constr, query);
}
In DataManager Class i am executing the query string.
public static void RunExecuteNonQuery(string Constr, string query)
{
OleDbConnection myConnection = new OleDbConnection(Constr);
try
{
myConnection.Open();
OleDbCommand myCommand = new OleDbCommand(query, myConnection);
myCommand.ExecuteNonQuery();
}
catch (Exception ex)
{
string Message = ex.Message;
throw ex;
}
finally
{
if (myConnection.State == ConnectionState.Open)
myConnection.Close();
}
}
private void toolstModify_Click_1(object sender, EventArgs e)
{
txtamcode.Enabled = true;
jewellery.LM_code = txtamcode.Text;
jewellery.M_Name = txtaccname.Text;
jewellery.Desc = txtdesc.Text;
jewellery.Modify();
MessageBox.Show("Data Updated Succesfully");
}

This annoyed me, screwy little OleDB, so I'll post my solution here for posterity. It's an old post but seems like a good place.
OleDB doesn't recognize named parameters, but it apparently does recognize that you're trying to convey a named parameter, so you can use that to your advantage and make your SQL semantic and easier to understand. So long as they're passed in the same order, it'll accept a variable as a named parameter.
I used this to update a simple Access database in a network folder.
using (OleDbConnection conn = new OleDbConnection(connString))
{
conn.Open();
OleDbCommand cmd = conn.CreateCommand();
for (int i = 0; i < Customers.Count; i++)
{
cmd.Parameters.Add(new OleDbParameter("#var1", Customer[i].Name))
cmd.Parameters.Add(new OleDbParameter("#var2", Customer[i].PhoneNum))
cmd.Parameters.Add(new OleDbParameter("#var3", Customer[i].ID))
cmd.Parameters.Add(new OleDbParameter("#var4", Customer[i].Name))
cmd.Parameters.Add(new OleDbParameter("#var5", Customer[i].PhoneNum))
cmd.CommandText = "UPDATE Customers SET Name=#var1, Phone=#var2" +
"WHERE ID=#var3 AND (Name<>#var4 OR Phone<>#var5)";
cmd.ExecuteNonQuery();
cmd.Parameters.Clear();
}
}
It may look like an excess of code, and yes you're technically repeating yourself, but this makes it worlds easier when you're playing connect-the-dots later on.....

You are close with the rest of your connection and such, but as you note, doing it with parameterized queries is safer from SQL-Injection...
// Some engines used named parameters, others may not... The "?"
// are "place-holders" for the ordinal position of parameters being added...
String MyQuery = "Update MyTable set SomeField = ?, AnotherField = ? "
+ " where YourKeyField = ?";
OleDbCommand MyUpdate = new OleDbCommand( MyQuery, YourConnection );
// Now, add the parameters in the same order as the "place-holders" are in above command
OleDbParameter NewParm = new OleDbParameter( "ParmForSomeField", NewValueForSomeField );
NewParm.DbType = DbType.Int32;
// (or other data type, such as DbType.String, DbType.DateTime, etc)
MyUpdate.Parameters.Add( NewParm );
// Now, on to the next set of parameters...
NewParm = new OleDbParameter( "ParmForAnotherField", NewValueForAnotherField );
NewParm.DbType = DbType.String;
MyUpdate.Parameters.Add( NewParm );
// finally the last one...
NewParm = new OleDbParameter( "ParmForYourKeyField", CurrentKeyValue );
NewParm.DbType = DbType.Int32;
MyUpdate.Parameters.Add( NewParm );
// Now, you can do you
MyUpdate.ExecuteNonQuery();

Just to add to RJB's answer, it's a little-known fact that OleDb actually DOES accept named parameters. You've just got to declare the parameters in SQL as well.
See: low-bandwidth.blogspot.com.au/2013/12/positional-msaccess-oledb-parameters.html
If you DON'T declare the parameters in SQL, OleDb uses purely positional parameter insertion, and it doesn't matter if the names of the parameters match the SQL, or if parameters are used twice in the SQL - it will just go through and blindly replace any found parameters in the SQL in order from start to end, with those passed.
However if you DO declare the parameters correctly, you get the benefit of named parameters and parameters allowed to be repeated multiple times within the SQL statement.