script.js

const gems = [
    {name: 'ruby', price: 10},
    {name: 'emerald', price: 20},
    {name: 'diamond', price: 30}
];
const store = [
    {gem: 'ruby', amount: 10},
    {gem: 'emerald', amount: 12},
    {gem: 'ruby', amount: 15},
    {gem: 'diamond', amount: 24}
];
const db = window.openDatabase('data', '1.0', 'data', 1*1024*1024);
db.transaction(t => {
    t.executeSql('CREATE TABLE gems (name TEXT, price INTEGER)');
    t.executeSql('CREATE TABLE store (gem TEXT, amount INTEGER)');
    for (let g of gems) {
        t.executeSql('INSERT INTO gems (name, price) VALUES (?, ?)',
        [g.name, g.price]);
    }
    for (let s of store) {
        t.executeSql('INSERT INTO store (gem, amount) VALUES (?, ?)', 
        [s.gem, s.amount]);
    }
}, e => console.error(e));
db.transaction(t => t.executeSql(
    'SELECT g.name, SUM(g.price*s.amount) total FROM gems g ' +
    'INNER JOIN store s ON g.name = s.gem GROUP BY 1', [],
    (t, result) => console.log(result.rows)
));