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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.

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.

String field with single quotation mark is causing an error when inserting record in table

I have below code:
query = "insert into tblB2B_OrderStatusTopStillInRB (LSRNbr, ShipName, Units, DroppedInRB, EPT, Status, OnTimeStatus, ShipVia, DroppedInRB_Order, RealEPT) ";
query += "values ('"
+ ListOrdStatusTopInRB[i].LSRNbr + "','"
+ ListOrdStatusTopInRB[i].ShipName + "',"
+ ListOrdStatusTopInRB[i].Units + ",'"
+ ListOrdStatusTopInRB[i].DroppedInRB + "','"
+ ListOrdStatusTopInRB[i].EPT + "','"
+ ListOrdStatusTopInRB[i].Status + "','"
+ ListOrdStatusTopInRB[i].OnTimeStatus + "','"
+ ListOrdStatusTopInRB[i].ShipVia + "','"
+ ListOrdStatusTopInRB[i].DroppedInRB_Order + "','"
+ ListOrdStatusTopInRB[i].RealEPT + "')";
cmd.CommandText = query;
cmd.ExecuteNonQuery();
And I just realized, that when the ShipName has a value with a single quotation mark, is causing an error in the insert statement, for instance: int'l Transp.
Is there any way to fix that, without removing the single quotation mark from the string?
I was trying using the following but didn't work:
cmd.CommandText = #query
+ #ListOrdStatusTopInRB[i].ShipName + "',"
Any ideas?

Is there any way to fix that, without removing the single quotation mark from the string?
Yes - use parameterized SQL instead. You should never use variable values directly in your SQL like this. It can allow SQL injection attacks, cause conversion oddities, and generally make the SQL more confusing to read.
See the documentation for SqlCommand.Parameters for an example of parameterized SQL.
Basically, the idea is that your SQL includes references to parameters, e.g.
INSERT INTO SomeTable(Foo, Bar) VALUES (#Foo, #Bar)
and then you specify the values for #Foo and #Bar separately. The values then aren't part of the SQL itself, so it doesn't matter whether or not they contain characters which would have special meaning within the SQL.

SQL statement, OleDbException error INSERT

There is no error in the code, but no information is appearing in the database.
string mysql;
mysql = "INSERT INTO Cars(Make,Model,Price,[Image]) VALUES ('"
+ tbMake.Text + "','" + tbModel.Text + "'," + tbPrice.Text + ",'" + FileUpload1.FileName + "')";
siteDB.InsertCommand = mysql;
DataList1.DataBind();
Cheers.

With an Access database the word IMAGE is a reserved keyword.
If you want to use it you need to encapsulate with square brakets
"INSERT INTO Cars(Make,Model,Price,[Image]) VALUES ......"
This will resolve you immediate problem, but as John Skeet pointed out in its comment you need to use a parametrized query because this solves also the problem of proper formatting of your text values.
What happens to your handy crafted query if a model name (or make) contains a single quote?
Another syntax error is waiting for you (and from my experience it will bite you just when you have finished to code and are ready to work)
Just to complete the answer, feel free to test if in this way it adds the record to your db
mysql = "INSERT INTO Cars(Make,Model,Price,[Image]) VALUES (?,?,?,?)";
OleDbCommand cmd = new OleDbCommand(mysql, con);
cmd.Parameters.AddWithValue("#p1", tbMake.Text);
cmd.Parameters.AddWithValue("#p2", tbModel.Text);
cmd.Parameters.AddWithValue("#p3", Convert.ToDecimal(tbPrice.Text));
cmd.Parameters.AddWithValue("#p4", FileUpload1.FileName);
cmd.ExecuteNonQuery();

I am assuming siteDB is an SQLDataAdapter.
In this case your code should at least be changed to this:
string mysql;
mysql = "INSERT INTO Cars(Make,Model,Price,Image) VALUES ('"
+ tbMake.Text + "','" + tbModel.Text + "'," + tbPrice.Text + ",'" + FileUpload1.FileName + "')";
siteDB.InsertCommand = mysql;
DataList1.DataBind();