You have an error in your SQL syntax (...) near ; - mysql

Question

I got this message, and I couldn't find any error:
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 'where id ='null'' at line 1
I assumed this code was wrong, but it turned out it isn't.
ResultSet rs = stmt.executeQuery("select password" +
"from userinfo where id = '" + id + "';");
This is full code of error file.
private boolean checkLoginInfo(String id, String password) throws ServletException
{
Connection conn = null;
Statement stmt = null;
try
{
Class.forName("com.mysql.jdbc.Driver");
conn = DriverManager.getConnection(
"jdbc:mysql://localhost:3306/webdb", "root", "1234");
if (conn == null)
throw new Exception("can't connect to database.<BR>");
stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery("select password" +
" from userinfo where id = '" + id + "';");
if (!rs.next())
return false;
String correctPassword = rs.getString("password");
if (password.equals(correctPassword))
return true;
else
return false;
}

Answer 1

There is a missing space between password and from:
select password" + "from userinfo where id = '" + id + "';"
Try this:
"SELECT password FROM `userinfo` WHERE id = '"+id+"'"
You should furthermore read about:
Escaping SQL queries
Authentication/Authorization (why do you select the password only?)
Code formatting
Edit 1:
The error messages tells us, you are setting the id to 'null' (String, because of ''), not NULL. If your id is expecting an Integer, but you are providing a String, it will break.