Question

I’m writing on a small Android App with SQLite 3 support. ATM I’m implementing some DB-Functions and asking myself if it is better have one big joined query or if it is OK to use multiple queries in respect to App performance.

Let’s say I have a 3 Tables “drivers”, “driven_runs”, “race_disciplines”. Every driven_run has a driver and a race_discipline. Let’s assume I want to get all race disciplines by a certain driver in a certain discipline.

Solution 1

I already coded a function getDriver(driverID) with a Driver-Object in return and a function getRaceDiscipline(disciplineID) with a Race Discipline in return. So I would just create a function

public ArrayList<DrivenRun> getDrivenRunsOnDiscipline(short driverID, short disciplineID) {
    ArrayList<DrivenRun> drivenRuns = new ArrayList<DrivenRun>();
    String sql = "SELECT * FROM " + DBHelper.TABLE_DRIVEN_RUNS + " WHERE " 
            + DBHelper.DRIVEN_RUNS_COLUMN_DRIVER_ID + "=" + driverID + " AND " 
            + DBHelper.DRIVEN_RUNS_COLUMN_RACE_DISCIPLINE_ID + "=" + disciplineID + ";";
    Cursor result = rawQuery(sql);
    if (result.moveToFirst()) {
        do {
            Driver driver = getDriver(driverID);
            RaceDiscipline discipline = getRaceDiscipline(disciplineID);
            DrivenRun run = new DrivenRun();
            run.setDriver(driver);
            run.setDiscipline(discipline);
            run.setResult("WHATEVER");
            drivenRuns.add(run);
        } while(result.moveToNext());
    }
    return drivenRuns;
}

in this case there would be 3 queries executed on after another but the coding is much more simple.

Solution 2

I would create one big joined query like

String sql = "SELECT * FROM driven_runs CROSS JOIN drivers CROSS_JOIN race_disciplines WHERE driven_runs.driver_id=drivers.id AND driven_runs.race_discipline_id=race_disciplines.id"
Cursor result = rawQuery(sql);

and would manually create the Driver and DrivenRun Object.

This solution needs much more writing but only one query is executed (or does the DB executes 3 queries as well when joining 3 tables?)

Long story short, is it OK to go with solution 1 because in regards to performance there isn’t much of a difference?

Answer 1

In general, go for the simpler code until there’s a good performance reason not to. Given that this is SQLite anyway, I don’t think there’s likely to be much performance difference, since the overhead for queries is pretty low.

Premature optimization is the root of all evil.