Added some spatial query for plain sql backend.

common/coords.go

@@ -37,6 +37,34 @@ func (c Coord) Equals(o Coord) bool {
 	return c.X == o.X && c.Y == o.Y && c.Z == o.Z
 }
 
+func minComponent(a, b int16) int16 {
+	if a < b {
+		return a
+	}
+	return b
+}
+
+func maxComponent(a, b int16) int16 {
+	if a > b {
+		return a
+	}
+	return b
+}
+
+func MinCoord(a, b Coord) Coord {
+	return Coord{
+		X: minComponent(a.X, b.X),
+		Y: minComponent(a.Y, b.Y),
+		Z: minComponent(a.Z, b.Z)}
+}
+
+func MaxCoord(a, b Coord) Coord {
+	return Coord{
+		X: maxComponent(a.X, b.X),
+		Y: maxComponent(a.Y, b.Y),
+		Z: maxComponent(a.Z, b.Z)}
+}
+
 // Constructs a database key out of byte slice.
 func DecodeStringFromBytes(key []byte) (pos int64, err error) {
 	return strconv.ParseInt(string(key), 10, 64)