use subquery to get first records if DISTINCT is used (in Oracle compiler)

2 files changed, 10 insertions, 2 deletions

diff --git a/lib/arel/engines/sql/compilers/oracle_compiler.rb b/lib/arel/engines/sql/compilers/oracle_compiler.rb
index ce575c2170..560022445a 100644
--- a/lib/arel/engines/sql/compilers/oracle_compiler.rb
+++ b/lib/arel/engines/sql/compilers/oracle_compiler.rb
@@ -5,9 +5,9 @@ module Arel
       def select_sql
         where_clauses_array = where_clauses
         if limit_or_offset = !taken.blank? || !skipped.blank?
-          # if need to select first records without ORDER BY and GROUP BY
+          # if need to select first records without ORDER BY and GROUP BY and without DISTINCT
           # then can use simple ROWNUM in WHERE clause
-          if skipped.blank? && groupings.blank? && orders.blank?
+          if skipped.blank? && groupings.blank? && orders.blank? && select_clauses[0] !~ /^DISTINCT /
             where_clauses_array << "ROWNUM <= #{taken}" if !taken.blank? && skipped.blank? && groupings.blank? && orders.blank?
             limit_or_offset = false
           end
diff --git a/spec/engines/sql/unit/relations/take_spec.rb b/spec/engines/sql/unit/relations/take_spec.rb
index 9f2967a0bd..cc3c3dbbf5 100644
--- a/spec/engines/sql/unit/relations/take_spec.rb
+++ b/spec/engines/sql/unit/relations/take_spec.rb
@@ -34,6 +34,14 @@ module Arel
             ORDER BY "USERS"."ID" ASC)
             where rownum <= 4
           })
+
+          sql_with_distinct = Take.new(@relation.project('DISTINCT "USERS"."ID"'), @taken).to_sql
+          sql_with_distinct.should be_like(%Q{
+            select * from
+            (SELECT DISTINCT "USERS"."ID"
+            FROM "USERS")
+            where rownum <= 4
+          })
         end
 
         adapter_is_not :mysql, :oracle do