add order by

Sources/SQLite/Query/SQLiteQuery+Select.swift

@@ -29,23 +29,44 @@ extension SQLiteQuery {
         public var columns: [ResultColumn]
         public var tables: [TableOrSubquery]
         public var predicate: Expression?
+        public var orderBy: [OrderBy]
 
         public init(
             with: WithClause? = nil,
             distinct: Distinct? = nil,
             columns: [ResultColumn] = [],
             tables: [TableOrSubquery] = [],
-            predicate: Expression? = nil
+            predicate: Expression? = nil,
+            orderBy: [OrderBy] = []
         ) {
             self.with = with
             self.distinct = distinct
             self.columns = columns
             self.tables = tables
             self.predicate = predicate
+            self.orderBy = orderBy
+        }
+    }
+}
+
+extension SQLiteQuery {
+    public struct OrderBy {
+        public var expression: Expression
+        public var direction: Direction
+
+        public init(expression: Expression, direction: Direction) {
+            self.expression = expression
+            self.direction = direction
         }
     }
 }
 
+extension SQLiteSerializer {
+    func serialize(_ orderBy: SQLiteQuery.OrderBy, _ binds: inout [SQLiteData]) -> String {
+        return serialize(orderBy.expression, &binds) + " " + serialize(orderBy.direction)
+    }
+}
+
 extension SQLiteSerializer {
     func serialize(_ select: SQLiteQuery.Select, _ binds: inout [SQLiteData]) -> String {
         var sql: [String] = []
@@ -65,6 +86,10 @@ extension SQLiteSerializer {
             sql.append("WHERE")
             sql.append(serialize(predicate, &binds))
         }
+        if !select.orderBy.isEmpty {
+            sql.append("ORDER BY")
+            sql.append(select.orderBy.map { serialize($0, &binds) }.joined(separator: ", "))
+        }
         return sql.joined(separator: " ")
     }