from qgis.core import *
from qgis.gui import *
from qgis.utils import *
from PyQt4.QtCore import *
from PyQt4.QtGui import *

import processing
from processing.core.Processing import Processing

uri = QgsDataSourceURI()

uri.setConnection("localhost", "5432", "dbName", "user", "pass")

uri.setDataSource("public", "Dzialki", "geom")
layer1 = QgsVectorLayer(uri.uri(), "tbName", "postgres")

uri.setDataSource("public", "inwentaryzacja RD3 - 2015", "geom")
layer2 = QgsVectorLayer(uri.uri(), "tbName", "postgres")

processing.runalg("qgis:joinattributesbylocation",{
                       "TARGET": inwentarizationLayer,
                        "JOIN": plotsLayer,
                        "PREDICATE":u'intersects',
                        "SUMMARY":0,
                        "KEEP":0,
                       "OUTPUT":"path"})

vl = QgsVectorLayer("path", "name", "ogr")

#QgsMapLayerRegistry.instance().addMapLayers([layer1, layer2, vl])

saveUri = "dbname='dbname' host=localhost port=5432 user='user' password='pass' key=gid type=POINT table="public"."test" (geom) sql="
crs_id = 4326
crs = QgsCoordinateReferenceSystem(crs_id, QgsCoordinateReferenceSystem.EpsgCrsId)
error = QgsVectorLayerImport.importLayer(vl, saveUri, "postgres", crs, False, False)

imports

qgs = QgsApplication([], True)
qgs.setPrefixPath("path", True)
qgs.initQgis()

code..

QgsApplication.exitQgis()