SQL Syntax Problems - mysql

Question

Im trying to do this:
String insertQuery=" DELETE FROM Accounts WHERE Username= " + Username + ";";
But im getting this error:
com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Unknown column 'sam' in 'where clause'
Its getting the right username etc I know this by testing, I assume the syntax is wrong but im getting no syntax errors?
The table is called Accounts. The coloums are Username & Password,

Answer 1

You are missing single quotes. In your case(it's string) variable need to be wrapped in them or it'll be interpreted as column.
String insertQuery = "DELETE FROM Accounts WHERE Username = '" + Username + "'";
Recommendation:
Hence i recommend you to use placeholders to avoid this kind of problem. Don't forget to care about a security(SQL Injection for instance). It's worth to say that parametrized statements are also more human-readable, safer and faster as well.
I don't like "hardcoded" queries. Let's imagine a scenario if you had a table with ten columns and imagine how you query will look in this case: absolutely human-unreadable.
An usage of parametrized statements is always very efficient and comfortable practise. Your code looks good and becomes human-readable and what is "main" solution is much more safer and cleaner.
Have look at PreparedStatements. Basic example:
private final String deleteQuery = "DELETE FROM Accounts WHERE Username = ?";
public boolean deleteObject(String username) {
Connection c = null;
PreparedStatement ps = null;
try {
c = DataSource.getConnection();
ps = c.prepareStatement(deleteQuery);
ps.setString(1, username); // numbering starts with 1 not 0!
return ps.executeUpdate() > 0;
}
catch (SQLException ex) {
System.out.println("Error in deleteObject() method: " + ex.getMessage());
return false;
}
finally {
if (c != null) {
try {
c.close();
}
catch (SQLException ex) {
System.out.println("Error in closing conn: " + ex.getMessage());
}
}
}
}

Answer 2

If username is a varchar you need to add single quotes around the value in the where clause.
String insertQuery=" DELETE FROM Accounts WHERE Username= '" + Username + "';";
Since the value is not quoted its identifying the username, I'm assuming its Sam as a column.