Android: Distinct and GroupBy in ContentResolver

Question

What would be a sensible way to add DISTINCT and/or GROUPBY to ContentResolver- based queries. Right now I have to create custom URI for each special case. Is there a better way? (I still program for 1.5 as lowest common denominator)

Answer 1

Since no one came to answer I'm just going to tell how I solved this. Basically I would create custom URI for each case and pass the criteria in selection parameter. Then inside ContentProvider#query I would identify the case and construct raw query based on table name and selection parameter.

Here's quick example:

switch (URI_MATCHER.match(uri)) {
    case TYPES:
        table = TYPES_TABLE;
        break;
    case TYPES_DISTINCT:
        return db.rawQuery("SELECT DISTINCT type FROM types", null);
    default:
        throw new IllegalArgumentException("Unknown URI " + uri);
    }
    return db.query(table, null, selection, selectionArgs, null, null, null);

Answer 2

You can do nice hack when querying contentResolver, use:

String selection = Models.SOMETHING + "=" + something + ") GROUP BY (" + Models.TYPE;

Answer 3

If you want to use DISTINCT with SELECT more then one column, You need to use GROUP BY.
Mini Hack over ContentResolver.query for use this:

Uri uri = Uri.parse("content://sms/inbox");
        Cursor c = getContentResolver().query(uri, 
            new String[]{"DISTINCT address","body"}, //DISTINCT
            "address IS NOT NULL) GROUP BY (address", //GROUP BY
            null, null);
        if(c.moveToFirst()){
            do{
                Log.v("from", "\""+c.getString(c.getColumnIndex("address"))+"\"");
                Log.v("text", "\""+c.getString(c.getColumnIndex("body"))+"\"");

            } while(c.moveToNext());
        }

This code select one last sms for each of senders from device inbox.
Note: before GROUP BY we always need to write at least one condition. Result SQL query string inside ContentResolver.query method will:

SELECT DISTINCT address, body FROM sms WHERE (type=1) AND (address IS NOT NULL) GROUP BY (address) 

Answer 4

In your overridden ContentProvider query method have a specific URI mapping to using distinct.

Then use SQLiteQueryBuilder and call the setDistinct(boolean) method.

@Override
public Cursor query(Uri uri, String[] projection, String selection,
        String[] selectionArgs, String sortOrder)
{
    SQLiteQueryBuilder qb = new SQLiteQueryBuilder();

    boolean useDistinct = false;

    switch (sUriMatcher.match(uri))
    {
    case YOUR_URI_DISTINCT:
        useDistinct = true;
    case YOUR_URI:
        qb.setTables(YOUR_TABLE_NAME);
        qb.setProjectionMap(sYourProjectionMap);
        break;

    default:
        throw new IllegalArgumentException("Unknown URI " + uri);
    }

    // If no sort order is specified use the default
    String orderBy;
    if (TextUtils.isEmpty(sortOrder))
    {
        orderBy = DEFAULT_SORT_ORDER;
    }
    else
    {
        orderBy = sortOrder;
    }
    // Get the database and run the query
    SQLiteDatabase db = mDBHelper.getReadableDatabase();
            // THIS IS THE IMPORTANT PART!
    qb.setDistinct(useDistinct);
    Cursor c = qb.query(db, projection, selection, selectionArgs, null, null, orderBy);

    if (c != null)
    {
        // Tell the cursor what uri to watch, so it knows when its source data changes
        c.setNotificationUri(getContext().getContentResolver(), uri);
    }

    return c;
}

Answer 5

Though I have not used Group By, I have used Distinct in content resolver query.

Cursor cursor = contentResolver .query(YOUR_URI, new String[] {"Distinct "+ YOUR_COLUMN_NAME}, null, null, null);

Answer 6

In some condition, we can use "distinct(COLUMN_NAME)" as the selection, and it work perfect. but in some condition, it will cause a exception.

when it cause a exception, i will use a HashSet to store the column values....

Answer 7

// getting sender list from messages into spinner View
    Spinner phoneListView = (Spinner) findViewById(R.id.phone_list);
    Uri uri = Uri.parse("content://sms/inbox");     
    Cursor c = getContentResolver().query(uri, new String[]{"Distinct address"}, null, null, null);
    List <String> list;
    list= new ArrayList<String>();
    list.clear();
    int msgCount=c.getCount();
    if(c.moveToFirst()) {
        for(int ii=0; ii < msgCount; ii++) {
            list.add(c.getString(c.getColumnIndexOrThrow("address")).toString());
            c.moveToNext();
        }
    }
    phoneListView.setAdapter(new ArrayAdapter<String>(BankActivity.this, android.R.layout.simple_dropdown_item_1line, list));

Answer 8

Adding the Distinct keyword in the projection worked for me too, however, it only worked when the distinct keyword was the first argument:

String[] projection = new String[]{"DISTINCT " + DBConstants.COLUMN_UUID, ... };

Answer 9

Maybe its more simple to get distinct values, try to add the DISTINCT word before the column name you want into the projection table

String[] projection = new String[]{
                BaseColumns._ID,
                "DISTINCT "+ Mediastore.anything.you.want
};

and use it as an argument to query method of the content resolver!

I hope to help you, cause I have the same question before some days