SUM¶
The Sum
aggregate function allows you to calculate the mathematical sum for a set of objects. To use the function, include Sum(columnNameInDatabase)
into the list of properties requested from the server. For example, the following query retrieves the sum for all box office earnings for all movies in the database:
DataQueryBuilder dataQueryBuilder = DataQueryBuilder.create().setProperties( "Sum(totalBoxOffice)");
Backendless.Data.of( "Movie" ).find( dataQueryBuilder, new AsyncCallback<List<Map>>()
{
@Override
public void handleResponse( List<Map> response )
{
// print out the first object from the collection
Log.i( "MYAPP", response.get( 0 ) );
}
@Override
public void handleFault( BackendlessFault fault )
{
Log.e( "MYAPP", fault.toString() );
}
});
sum
property in the returned object. The value of the property is the mathematical sum of all values in the totalBoxOffice
column:
Using Alias¶
To change the name of the returned property from sum
to a custom name, use the following syntax:
Sum( columnNameInDatabase ) as customPropertyName
For example, the following query returns the sum value in the grandTotal
property:
DataQueryBuilder dataQueryBuilder = DataQueryBuilder.create();
dataQueryBuilder.setProperties( "Sum(totalBoxOffice) as grandTotal" );
Backendless.Data.of( "Movie" ).find( dataQueryBuilder, new AsyncCallback<List<Map>>()
{
@Override
public void handleResponse( List<Map> response )
{
// print out the first object from the collection
Log.i( "MYAPP", response.get( 0 ) );
}
@Override
public void handleFault( BackendlessFault fault )
{
Log.e( "MYAPP", fault.toString() );
}
});
grandTotal
property:
Grouping Results¶
Results in the response can be grouped by values from another column. To request grouping of the results, add the groupBy
parameter to the request with the value containing the name of the column. For example, the following request returns the sum of earnings value for the movies in the database grouped by the year the movies were released:
DataQueryBuilder dataQueryBuilder = DataQueryBuilder.create();
dataQueryBuilder.setProperties( "Sum(totalBoxOffice)", "yearReleased" );
dataQueryBuilder.setGroupBy( "yearReleased" );
Backendless.Data.of( "Movie" ).find( dataQueryBuilder, new AsyncCallback<List<Map>>()
{
@Override
public void handleResponse( List<Map> response )
{
Log.i( "MYAPP", response );
}
@Override
public void handleFault( BackendlessFault fault )
{
Log.e( "MYAPP", fault.toString() );
}
});
Sorting¶
The results can be sorted using the sortBy
parameter. For example, results for the following request will be sorted by the values in the yearReleased
column in the descending order:
DataQueryBuilder dataQueryBuilder = DataQueryBuilder.create();
dataQueryBuilder.setProperties( "Sum(totalBoxOffice)", "yearReleased" );
dataQueryBuilder.setGroupBy( "yearReleased" );
dataQueryBuilder.setSortBy( "yearReleased DESC" );
Backendless.Data.of( "Movie" ).find( dataQueryBuilder, new AsyncCallback<List<Map>>()
{
@Override
public void handleResponse( List<Map> response )
{
Log.i( "MYAPP", response );
}
@Override
public void handleFault( BackendlessFault fault )
{
Log.e( "MYAPP", fault.toString() );
}
});
DataQueryBuilder dataQueryBuilder = DataQueryBuilder.create();
dataQueryBuilder.setProperties( "Sum(totalBoxOffice) as grandTotal", "yearReleased" );
dataQueryBuilder.setGroupBy( "yearReleased" );
dataQueryBuilder.setSortBy( "grandTotal" );
Backendless.Data.of( "Movie" ).find( dataQueryBuilder, new AsyncCallback<List<Map>>()
{
@Override
public void handleResponse( List<Map> response )
{
Log.i( "MYAPP", response );
}
@Override
public void handleFault( BackendlessFault fault )
{
Log.e( "MYAPP", fault.toString() );
}
});