regex.js

var tests = [
    "countries",
    "'10m_admin_0_countries'",
    '(SELECT countries.* FROM countries)',
    '(SELECT countries.*, bus2.factor FROM countries LEFT JOIN business.bus2 ON countries.adm0_a3 = bus2.iso)',
    '(SELECT countries.*, bus2.factor FROM countries LEFT JOIN business.bus2 ON countries.adm0_a3 = bus2.iso WHERE foo = bar)',
    '(SELECT countries.*, bus2.factor FROM countries LEFT JOIN business.bus2 ON countries.adm0_a3 = bus2.iso LEFT JOIN business.bus2 ON countries.adm0_a3 = bus2.iso WHERE foo = bar)',
    '(SELECT countries.*, bus2.factor FROM countries LEFT JOIN business.bus2 ON countries.adm0_a3 = bus2.iso WHERE foo = bar LIMIT 3)'];
function m(t) {
    var parts = t.replace(/^\(|\)$/g, '')
        .split(/WHERE/i).shift()
        .split(/FROM/i).pop()
        .split(/(LEFT|INNER|RIGHT)\s+JOIN/i),
        tables = [];
    for (var i = 0; i < parts.length; i++) {
        if (i % 2 == 0) {
            tables.push(parts[i].split(/ON/i).shift().split('.').pop().replace(/^\s*|\s*$/g, ''));
        }
    }
    console.log(tables);
}
for (i = 0; i < tests.length; i++) {
    m(tests[i]);
}