can’t find MySql.Data.MySqlClient.MySqlException insert query error

This is the error message

MySql.Data.MySqlClient.MySqlException: 'You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '''')' at line 1'

this is my query

MySqlCommand cmd = new MySqlCommand("insert into subject(id, code, title, unit) values('" + textBox1.Text + "',''" + textBox2.Text + "',''" + textBox3.Text + "',''" + textBox4.Text + "')", conn);

I’ve been looking over at it for over an hour now and I still get this error

Answer

Besides for @Kazi’s answer for fixing the incorrect query.

Alternatively, it is recommended to use Parameterized Query.

UPDATED: As suggested by @CodeCaster for the concerns mentioned in Stop Using AddWithValue() article, I switch all the AddWithValue() to Add("@Parameter", SqlDbType).Value

MySqlCommand cmd = new MySqlCommand("insert into subject(id, code, title, unit) values(@ID, @Code, @Title, @Unit)", conn);
cmd.Parameters.Add("@ID", SqlDbType.int).Value = textBox1.Text;
cmd.Parameters.Add("@Code", SqlDbType.Varchar, 10).Value = textBox2.Text;
cmd.Parameters.Add("@Title", SqlDbType.NVarchar, 50).Value = textBox3.Text;
cmd.Parameters.Add("@Unit", SqlDbType.Varchar).Value = textBox4.Text;

And also be sure that the value you pass with the SqlDbType must match the data type as respective database table column.

The reasons to use Parameterized Query are:

  1. It simplifies the query in pass the parameters and makes the query become more readable.
  2. Prevent SQL Injection.

Reference: Prepare MySQL Statement