revert PR #1290, closes #1312

Author: Roman A. Grigorovich

drivers/sqlboiler-psql/driver/override/main/17_upsert.go.tpl

@@ -103,7 +103,11 @@ func (o *{{$alias.UpSingular}}) Upsert({{if .NoContext}}exec boil.Executor{{else
 		}
 
 		conflict := conflictColumns
-		if len(conflict) == 0 {
+		if len(conflict) == 0 && updateOnConflict && len(update) != 0 {
+			if len({{$alias.DownSingular}}PrimaryKeyColumns) == 0 {
+				return errors.New("{{.PkgName}}: unable to upsert {{.Table.Name}}, could not build conflict column list")
+			}
+
 			conflict = make([]string, len({{$alias.DownSingular}}PrimaryKeyColumns))
 			copy(conflict, {{$alias.DownSingular}}PrimaryKeyColumns)
 		}

drivers/sqlboiler-psql/driver/override/main/singleton/psql_upsert.go.tpl

@@ -21,13 +21,16 @@ func buildUpsertQueryPostgres(dia drivers.Dialect, tableName string, updateOnCon
 		columns,
 	)
 
-	buf.WriteByte('(')
-	buf.WriteString(strings.Join(conflict, ", "))
+	if len(conflict) != 0 {
+		buf.WriteByte('(')
+		buf.WriteString(strings.Join(conflict, ", "))
+		buf.WriteString(") ")
+	}
 
 	if !updateOnConflict || len(update) == 0 {
-		buf.WriteString(") DO NOTHING")
+		buf.WriteString("DO NOTHING")
 	} else {
-		buf.WriteString(") DO UPDATE SET ")
+		buf.WriteString("DO UPDATE SET ")
 
 		for i, v := range update {
 		    if len(v) == 0 {