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How to sovle Query Issue throwing MySql.Data.MySqlClient.MySqlException

I am doing a project with C# and I have this error:
MySql.Data.MySqlClient.MySqlException (0x80004005): You have an error
in your SQL syntax; check the manual that corresponds to your MariaDB
server version for the right syntax to use near ' last_name= , email=
, phone= , address= WHERE id= 6' at line 1
I know this is a query error, but I tried many things and I don't see the issue.
My query is this:
cm = new MySqlCommand("UPDATE customers SET first_name= " + txtNombre.Text + "," + " last_name= " + txtApellidos.Text + "," + " email= " + txtEmail.Text + "," + " phone= " + txtTelefono.Text + "," + " address= " + txtDireccion.Text + " WHERE id= " + dgvClient.SelectedRows[0].Cells[0].Value.ToString() , con);

There should be single quotes around the text that you want to inject into the query, so it will look like this:
var query = "UPDATE customers SET first_name= '" + txtNombre.Text + "'";
This is the easiest solution but is advised against, mostly because of a possiblity for 'sql injection'. The easiest way to show this is by using the name O'Brian, because of the quote the database will think that the name is only O and then see it followed by Brian that it doesn't know what to do with and gives an error. Some people can use this to add other things to your query to cause harm to your database (like dropping tables or the whole database)
It is advised to use parameters, this solves this whole sql injection issue. Your code will look as follows:
cm = new MySqlCommand("UPDATE customers SET first_name=#first_name, last_name=#apellidos WHERE id=#id", con) ;
cm.Parameters.AddWithValue("#first_name", txtNombre.Text);
cm.Parameters.AddWithValue("#apellidos", txtApellidos.Text);
cm.Parameters.AddWithValue("#id", dgvClient.SelectedRows[0].Cells[0].Value.ToString());
It is best to always use parameters for your query, you can also look into using a framework like Entity Framework that does this automatically for you.

Error : in my query i am using multiple variables in c#

i am not getting what is the issue in the query probably i am not following the correct way to put the string and char sign , i am inserting the data in c# to local host with where clause please check the query and Error i am getting
Here is the query
String insertQuery = "insert into exam_add (id,session_id,Title,From_date,To_date,class_id,is_Post,is_Lock) select '"+id+ ",s.session,'" + title.Text+",'"+ from.Value.Date.ToString("yyyy-MM-dd")+",'"+to.Value.Date.ToString("yyyy-MM-dd")+ ", c.class_name,'"+x+",'"+x+" from year_session s, classes c where s.id = '1' and c.id='" + cls + "'";
Exception image
here the image for exception i am getting after run this query

On your ...'"+x+"... you forgot to close the single quotes. You open them but you never close them after you add the X variable to your query. All SQL is seeing is "'0," which is invalid syntax.

I recommend use SQLparameters to avoid sql injection but your error is you forgot to close the single quotes it shoud be like this '"+cls + "'
String insertQuery = "insert into exam_add (id,session_id,Title,From_date,To_date,class_id,is_Post,is_Lock) select '" + id + "','"+s.session+"','" + title.Text + "','" + from.Value.Date.ToString("yyyy-MM-dd") + "','" + to.Value.Date.ToString("yyyy-MM-dd")+"' , '"+c.class_name+"','" + x + "','" + x + "' from year_session s, classes c where s.id = '1' and c.id='" + cls + "'";
I don't know why you need that on select columns. and you provided insufficient information and code on your question.

How to fix "System.Data.OleDb.OleDbException: 'Syntax error in UPDATE statement.'"?

I have been getting a syntax error in my UPDATE datagridview code which happens to work in another .cs file. My group has been looking at different solutions online but everything won't work.
My group has been looking at different solutions online but everything won't seem to work.
{
connection.Open();
OleDbCommand cmd = connection.CreateCommand();
cmd.CommandType = CommandType.Text;
cmd.CommandText = "Update Table1 set treatment = '" + treat.Text + "', remarks = '" + appRemarks.Text + "', cost = '" + treatCost.Text + "', Time = '" + textBox2.Text + "' where lastName = '" + Lastname.Text + "' ";
cmd.ExecuteNonQuery();
connection.Close();
MessageBox.Show("Updated Successfully!");
}
The expected output should be Updated Successfully! and it should reflect in the database file after clicking the update button. Sometimes the output is "Microsoft Engine database" which does not save the changes.
The error says "System.Data.OleDb.OleDbException: 'Syntax error in UPDATE statement.'" pointing to cmd.ExecuteNonQuery();

First, never use string concatenation to build a query. You're asking for a SQL Injection attack. The biggest thing I could see here is make sure that only columns that are string columns (varchar, char, text, etc..) have single-quoted values. Is cost a number? If so then it should be:
, cost=" + treatCost.Text + ",
If cost is a number, also make sure that there isn't a currency amount in the input field. If someone puts in 1,422.00 it's not a number and will fail since , is for decoration.
If someone puts in $1422.00 it's not a number as $ is for decoration.
Either of these would fail the query.

This would happen if someone types an apostrophe into the remarks field, which SQL server will interpret as the ending quote of the string. But much worse things can happen if the user knows a bit of sql and wants to cause trouble. For example, putting '-- in the remarks will result in
Update Table1 set treatment = 'blah', remarks = ''-- where lastName = 'foobar'
which will overwrite every row in the table, not only the one containing foobar.
Use query parameters so that user-provided values can't be interpreted as query keywords and structure.
Instead of remarks = '" + appRemarks.Text + "' you will have remarks = #Remarks as well as
cmd.Parameters.Add("#Remarks", SqlDbType.NText).Value = appRemarks.Text;
and all the other user inputs likewise.

Incorrect syntax in T-SQL statement in c#

I have the following code:
USE [DB] INSERT INTO Extract2_EventLog VALUES (" + li.userId + ", '" + li.startTime.ToString() + "', '" + li.endTime.ToString() + "', '" + li.elapsedTime.ToString() + (li.actionType == ActionType.REPORT ? "', 'report')" : "', 'extract')', '" + status + "'");
When I run this, I get the following error:
{"Incorrect syntax near ', '.\r\nUnclosed quotation mark after the
character string ''."}
I can't see what I'm doing wrong.. Anyone?

Man....Where to start with this...
First off, you should be using stored procedures that accept parameters (variables from your application code). Second, you should have a dataaccess layer in your application separating database calls and your user interface. I can't possible stress enough how important this is and how bad your current approach is. You will forever be fighting problems like this until you correct it.
But to address the question as it was asked...Your error is because your query string is malformatted. Use the debugging tools to view the string before it is sent to the database and then you should be able to quickly determine what is wrong with it. To troubleshoot, you can always cut and paste that string into SSMS, refine it there, and then make the necessary changes to your c# code.

First of all look at the answer of Stan Shaw, next take a look at the comment of Jon Skeet!
The first thing to do is stop building SQL like that... right now. Use parameterized SQL and you may well find the problem just goes away... and you'll be preventing SQL Injection Attacks at the same time.
They sayed everything that's important and just for the sake of giving you a direct answer:
You have a status + "'"); at your code which needs to be changed to status + "')"; ...
...like this one:
string statement = "USE [DB] INSERT INTO Extract2_EventLog VALUES (" + li.userId + ", '" + li.startTime.ToString() + "', '" + li.endTime.ToString() + "', '" + li.elapsedTime.ToString() + (li.actionType == ActionType.REPORT ? "', 'report')" : "', 'extract')', '" + status + "')";

Instead of concatenating values into your query you should use a parameterized query or a stored procedure.
A rewrite of your code could be something like (depending on datatypes, etc):
string commandText = "INSERT INTO Extract2_EventLog (userId, startTime, endTime, elapsedTime, actionType, [status]) VALUES (#userId, #startTime, #endTime, #elapsedTime, #actionType, #status)";
using (SqlConnection connection = new SqlConnection(connectionString))
{
SqlCommand command = new SqlCommand(commandText, connection);
command.Parameters.AddWithValue("#userId", li.userId);
command.Parameters.AddWithValue("#startTime", li.startTime);
command.Parameters.AddWithValue("#endTime", li.endTime);
command.Parameters.AddWithValue("#elapsedTime", li.elapsedTime);
command.Parameters.AddWithValue("#actionType", li.actionType == ActionType.REPORT ? "report" : "extract");
command.Parameters.AddWithValue("#status", status);
connection.Open();
int rowsAffected = command.ExecuteNonQuery();
Console.WriteLine("RowsAffected: {0}", rowsAffected);
}

You've forgot the " at the beginning. So your code reverts sql with non sql.
AND your example seems to be incomplete.

C# OleDb sql "UPDATE, WHERE" exception

So I have the following code :
public static void WriteToDatabase(string sql,string value,int Amount, string URL)
{
int times = int.Parse(((dr)[dt.Columns[1]]).ToString()) + Amount;
sql = "UPDATE Words "+
" SET Amount = " + times +
" WHERE Word = " + value +
" AND Website = " + URL + ";";
myAdp = new OleDbDataAdapter();
myAdp.InsertCommand = new OleDbCommand(sql, myConn);
myAdp.InsertCommand.ExecuteNonQuery();
}
Which supposed to update a value in a pre-made Microsoft Access 2007 file,
and whenever I run the code they following OleDb exception occurs :
An unhandled exception of type 'System.Data.OleDb.OleDbException' occurred in System.Data.dll ,
Syntax error missing operator in query expression : 'Word = meta AND Website = http://www.twitch.tv/directory'."
"
So I've searched the web for common errors that could happen, and I couldn't find any,
I'll be glad if someone can find the mistake in the sql.
Thanks.

You absolutely should be using parameterized queries for this. That is the right way to pass values in.
Your problem is that your query is missing single quotes:
"UPDATE Words "+
" SET Amount = " + times +
" WHERE Word = '" + value + "'" +
" AND Website = '" + URL + "'"
But let me re-emphasize that although this should work, you should fix the code so it uses parameters

Assuming the Word field is a varchar, you have forgotten the necessary single quotes around the variable. " WHERE Word = '" + value + "'"