1 files changed, 67 insertions, 0 deletions
diff --git a/activerecord/lib/arel/visitors/oracle12.rb b/activerecord/lib/arel/visitors/oracle12.rb
new file mode 100644
index 0000000000..b092aa95e0
--- /dev/null
+++ b/activerecord/lib/arel/visitors/oracle12.rb
@@ -0,0 +1,67 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Visitors
+    class Oracle12 < Arel::Visitors::ToSql
+      private
+
+        def visit_Arel_Nodes_SelectStatement(o, collector)
+          # Oracle does not allow LIMIT clause with select for update
+          if o.limit && o.lock
+            raise ArgumentError, <<-MSG
+            'Combination of limit and lock is not supported.
+            because generated SQL statements
+            `SELECT FOR UPDATE and FETCH FIRST n ROWS` generates ORA-02014.`
+          MSG
+          end
+          super
+        end
+
+        def visit_Arel_Nodes_SelectOptions(o, collector)
+          collector = maybe_visit o.offset, collector
+          collector = maybe_visit o.limit, collector
+          collector = maybe_visit o.lock, collector
+        end
+
+        def visit_Arel_Nodes_Limit(o, collector)
+          collector << "FETCH FIRST "
+          collector = visit o.expr, collector
+          collector << " ROWS ONLY"
+        end
+
+        def visit_Arel_Nodes_Offset(o, collector)
+          collector << "OFFSET "
+          visit o.expr, collector
+          collector << " ROWS"
+        end
+
+        def visit_Arel_Nodes_Except(o, collector)
+          collector << "( "
+          collector = infix_value o, collector, " MINUS "
+          collector << " )"
+        end
+
+        def visit_Arel_Nodes_UpdateStatement(o, collector)
+          # Oracle does not allow ORDER BY/LIMIT in UPDATEs.
+          if o.orders.any? && o.limit.nil?
+            # However, there is no harm in silently eating the ORDER BY clause if no LIMIT has been provided,
+            # otherwise let the user deal with the error
+            o = o.dup
+            o.orders = []
+          end
+
+          super
+        end
+
+        def visit_Arel_Nodes_BindParam(o, collector)
+          collector.add_bind(o.value) { |i| ":a#{i}" }
+        end
+
+        def is_distinct_from(o, collector)
+          collector << "DECODE("
+          collector = visit [o.left, o.right, 0, 1], collector
+          collector << ")"
+        end
+    end
+  end
+end