mysql node js quest -- SELECT EXISTS query - mysql

Question

what is wrong with this logic?
var selectString = 'SELECT EXISTS(SELECT 1 FROM users WHERE user="'+username+'")';
var queryUserExists = connection.query(selectString);
var resultsLength = queryUserExists._results.length;
console.log(queryUserExists);
if(resultsLength > 0){
socket.write("fail user already exists"+"\r\n");
} else {
console.log('insert=');
var query = connection.query (
'INSERT INTO users '+
'SET user = ?, password = ?, token = ?',
[username, password, token]
);
socket.write("success"+"\r\n");
}
resultsLength is always returned zero.
What is the proper way to use this query?
returned object:
sql: 'SELECT 1 FROM users WHERE user = \'a new user is my name\' ORDER BY user LIMIT 1',
typeCast: true,
nestTables: false,
_resultSet: null,
_results: [],
_fields: [],
_index: 0,
_loadError: null }

Answer 1

The proper code: thanks to https://stackoverflow.com/users/722783/mahmoud-gamal for the database query that is optimized!
connection.query("SELECT 1 FROM users WHERE user = '"+username+"' ORDER BY user LIMIT 1", function (error, results, fields) {
if (error) {
console.log(error);
socket.write("fail internal error"+"\r\n");
}
if (results.length > 0) {
console.log('fail');
socket.write("fail user already exists"+"\r\n");
} else {
console.log('insert');
var query = connection.query (
'INSERT INTO users '+
'SET user = ?, password = ?, token = ?',
[username, password, token]
);
socket.write("success"+"\r\n");
}
console.log(results);
});

Answer 2

Try this:
SELECT 1
FROM users
WHERE EXISTS (SELECT 1
FROM users
WHERE user = 'username')
ORDER BY user
LIMIT 1;
Or: Why not:
SELECT 1
FROM users
WHERE user = 'username'
ORDER BY user
LIMIT 1;
Note that:
ORDER BY user
LIMIT 1;
Are just for performance.