allow multiple occurencies of builder statements (#50)

* allow multiple occurencies of builder statements
* fix readme

---------

Co-authored-by: Sergei Malykh <sergey.malykh@groupprice.ru>

README.md

@@ -77,6 +77,14 @@ builder.query.each do |t|
 end
 ```
 
+The same builder's statement may occur multiple times.
+
+```ruby
+builder = conn.build('(/*select*/ from books) union (/*select*/ from movies)').select('title').query
+
+# => (SELECT title from books) union (SELECT title from movies)
+```
+
 The builder predefined next _SQL Literals_
 
 | Method      | SQL Literal  |

lib/mini_sql/builder.rb

@@ -128,7 +128,7 @@ def count(field = '*')
           v
         end
 
-      unless sql.sub!("/*#{k}*/", joined)
+      unless sql.gsub!("/*#{k}*/", joined)
         raise "The section for the /*#{k}*/ clause was not found!"
       end
     end

test/mini_sql/builder_tests.rb

@@ -229,6 +229,12 @@ def test_sql_literal
     assert_equal(builder.to_sql, 'SELECT * FROM products WHERE id = 10')
   end
 
+  def test_sql_literal_multiple
+    builder = @connection.build("(select 1 AS x /*polymorphic_where*/) union all (select 2 AS x /*polymorphic_where*/)")
+    builder.sql_literal(polymorphic_where: 'where 1 = 1')
+    assert_equal(builder.to_sql, "(select 1 AS x where 1 = 1) union all (select 2 AS x where 1 = 1)")
+  end
+
   def test_sql_literal_for_builder
     user_builder = @connection.build("SELECT * FROM users /*where*/").where('id = ?', 10)
     builder = @connection.build("SELECT * FROM (/*user_table*/) AS t")