column_count and column_names

close result_set and statements
main entry points for exec_non_query and exec_query closing them when ready

spec/std/db/dummy_driver.cr

@@ -40,6 +40,14 @@ class DummyDriver < DB::Driver
       end
     end
 
+    def column_count
+      2
+    end
+
+    def column_name(index)
+      "c#{index}"
+    end
+
     private def read? : DB::Any?
       n = @values.not_nil!.next
       raise "end of row" if n.is_a?(Iterator::Stop)

src/db/database.cr

@@ -9,12 +9,35 @@ module DB
       @driver = @driver_class.new(@options)
     end
 
+    # :nodoc:
     def prepare(query)
       @driver.prepare(query)
     end
 
+    # :nodoc:
     def exec(query, *args)
       prepare(query).exec(*args)
     end
+
+    def exec_non_query(query, *args)
+      exec_query(query) do |result_set|
+        result_set.move_next
+      end
+    end
+
+    # :nodoc:
+    def exec_query(query, *args)
+      result_set = exec(query, *args)
+      yield result_set
+      result_set.close
+    end
+
+    def exec_query_each(query, *args)
+      exec_query(query) do |result_set|
+        result_set.each do
+          yield result_set
+        end
+      end
+    end
   end
 end

src/db/result_set.cr

@@ -11,8 +11,17 @@ module DB
       end
     end
 
+    def close
+      @statement.close
+    end
+
     abstract def move_next : Bool
 
+    abstract def column_count : Int32
+    abstract def column_name(index : Int32) : String
+
+    # abstract def column_type(index : Int32)
+
     # list datatypes that must be supported form the driver
     # users will call read(String) or read?(String) for nillables
     {% for t in DB::TYPES %}

src/db/statement.cr

@@ -3,6 +3,7 @@ module DB
     getter driver
 
     def initialize(@driver)
+      @closed = false
     end
 
     def exec(*args) : ResultSet
@@ -32,9 +33,24 @@ module DB
     protected def before_execute
     end
 
+    # Closes this statement.
+    def close
+      raise "Statement already closed" if @closed
+      @closed = true
+      on_close
+    end
+
+    # Returns `true` if this statement is closed. See `#close`.
+    def closed?
+      @closed
+    end
+
     # 1-based positional arguments
     protected abstract def add_parameter(index : Int32, value)
     protected abstract def add_parameter(name : String, value)
+
     protected abstract def execute : ResultSet
+    protected def on_close
+    end
   end
 end