Handle case of select_prepend after select_append

This previously failed on databases that don't support
SELECT column, *. Fix it by scanning the current selection list
for the WILDCARD object, and replacing it with qualified selections
(SELECT column, table.*), which all databases should support.

lib/sequel/dataset/query.rb

@@ -1367,14 +1367,28 @@ def _current_select(allow_plain_wildcard)
         cur_sel = if allow_plain_wildcard && supports_select_all_and_column?
           [WILDCARD].freeze
         else
-          tables = Array(@opts[:from]) + Array(@opts[:join])
-          tables.map{|t| i, a = split_alias(t); a || i}.map!{|t| SQL::ColumnAll.new(t)}.freeze
+          _current_select_column_all
         end
+      elsif !allow_plain_wildcard && cur_sel.include?(WILDCARD)
+        cur_sel = cur_sel.dup
+        index = cur_sel.index(WILDCARD)
+        cur_sel.delete(WILDCARD)
+        _current_select_column_all.each_with_index do |ca, i|
+          cur_sel.insert(index+i, ca)
+        end
+        cur_sel.freeze
       end
 
       cur_sel
     end
 
+    # An array of SQL::ColumnAll objects for all FROM and JOIN tables.  Used for select_append
+    # and select_prepend.
+    def _current_select_column_all
+      tables = Array(@opts[:from]) + Array(@opts[:join])
+      tables.map{|t| i, a = split_alias(t); a || i}.map!{|t| SQL::ColumnAll.new(t)}.freeze
+    end
+
     # If invert is true, invert the condition.
     def _invert_filter(cond, invert)
       if invert

spec/core/dataset_spec.rb

@@ -1507,6 +1507,11 @@ def supports_cte_in_subselect?; false end
     @d.select(Sequel::SQL::ColumnAll.new(:a)).select_prepend(Sequel::SQL::ColumnAll.new(:b)).sql.must_equal 'SELECT b.*, a.* FROM test'
   end
 
+  it "should work with an explicit selection of *" do
+    @d.select_append(:a).select_prepend(:b).sql.must_equal 'SELECT b, test.*, a FROM test'
+    @d.from(:t1, :t2).natural_join(:t3).select_append(:a).select_prepend(:b).sql.must_equal 'SELECT b, t1.*, t2.*, t3.*, a FROM t1, t2 NATURAL JOIN t3'
+  end
+
   it "should accept a block that yields a virtual row" do
     @d.select(:a).select_prepend{|o| o.b}.sql.must_equal 'SELECT b, a FROM test'
     @d.select(Sequel::SQL::ColumnAll.new(:a)).select_prepend(Sequel::SQL::ColumnAll.new(:b)){b(1)}.sql.must_equal 'SELECT b.*, b(1), a.* FROM test'

spec/integration/dataset_test.rb

@@ -192,6 +192,7 @@
 
   it "should support select_prepend and select_append" do
     @ds.select_prepend{number.as(:n)}.select_append{id.as(:i)}.first.to_a.must_equal [[:n, 10], [:id, 1], [:number, 10], [:i, 1]]
+    @ds.select_append{id.as(:i)}.select_prepend{number.as(:n)}.first.to_a.must_equal [[:n, 10], [:id, 1], [:number, 10], [:i, 1]]
   end
 
   it "should skip locked rows correctly" do