Fix a failing test in ppostgres backend
Fix a failing test in ppostgres backend

coreos/peewee,lez/peewee,jarrahwu/peewee,jnovinger/peewee,coreos/peewee,d1hotpep/peewee,Sunzhifeng/peewee,new-xiaji/peewee,teserak/peewee,d1hotpep/peewee,giserh/peewee,jnovinger/peewee,bopo/peewee,giserh/peewee,wenxer/peewee,Dipsomaniac/peewee,stas/peewee,Sunzhifeng/peewee,zhang625272514/peewee,new-xiaji/peewee,ghukill/peewee,new-xiaji/peewee,coleifer/peewee,bopo/peewee,bopo/peewee,mackjoner/peewee,fuzeman/peewee,Dipsomaniac/peewee,py4a/peewee,Dipsomaniac/peewee,coreos/peewee,jarrahwu/peewee,wenxer/peewee,coleifer/peewee,fuzeman/peewee,coleifer/peewee,zhang625272514/peewee,ronyb29/peewee,softside/peewee,zhang625272514/peewee,Sunzhifeng/peewee,jarrahwu/peewee