Web SQL - Combine two SELECT statements with a LIMIT using UNION

PG-WebSQL.js

for (var i = 0; i < testResults.length; i++){
    (function(i){
        db.transaction(function(tx){
            tx.executeSql(
            "SELECT * FROM ( " +
                "SELECT 'lab' AS table_name, id FROM lab_test_names " +
                "WHERE organizerClassId = ? " +
                "LIMIT 1 " +
            " ) " +
            "UNION " +
            "SELECT * FROM ( " + 
                "SELECT 'rad' AS table_name, id FROM radiology_test_names " +
                "WHERE organizerClassId = ? " +
                "LIMIT 1 " +
            " ) ",
            [testClassId[i], testClassId[i]],
                function(tx, results){
                    //console.log("JSON.stringify(results.rows.item(0)) ==> " + JSON.stringify(results.rows.item(0)) );
                    var tableName = results.rows.item(0).table_name;
                    if (tableName == "lab"){
                        console.log("this is a lab result entry");
                        // rest of my arithmetic below if this is a lab result...
                    } else { // else this is a radiology result entry
                        console.log("this is a radiology result entry");
                        // rest of my arithmetic below if this is a radiology result...
                    }
                },
                function(tx, err){
                    console.log("SQL Error");
                    if (err) {
                        console.log("ERROR " + err.code + ": " + err.message);
                    }
                }
            ); // end of tx.executeSql
        }); // end of db.transaction
    })(i) // closure
}