Javascript Web SQL中的重复数据

我怎样才能使数据不重复，无论自动插入id行如何

db.transaction(function (tx) {
    tx.executeSql('CREATE TABLE IF NOT EXISTS logins (Username, Password)');
});
db.transaction(function (tx) {
    tx.executeSql('INSERT INTO logins VALUES ("Ahmed","123")');
    tx.executeSql('INSERT INTO logins VALUES ("Ahmed","123")');
});

你可以试试

db.transaction(function (tx) {
    tx.executeSql('CREATE TABLE IF NOT EXISTS logins (Username UNIQUE, Password)');
    tx.executeSql('INSERT INTO logins VALUES ("Ahmed","123")');
    tx.executeSql('INSERT INTO logins VALUES ("Ahmed","123")');
});