1 files changed, 19 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
index caecbc9b3a..35df0a1542 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite_adapter.rb
@@ -222,6 +222,25 @@ module ActiveRecord
 
       # DATABASE STATEMENTS ======================================
 
+      def explain(arel)
+        sql = "EXPLAIN QUERY PLAN #{to_sql(arel)}"
+        ExplainPrettyPrinter.new.pp(exec_query(sql, 'EXPLAIN'))
+      end
+
+      class ExplainPrettyPrinter
+        # Pretty prints the result of a EXPLAIN QUERY PLAN in a way that resembles
+        # the output of the SQLite shell:
+        #
+        #   0|0|0|SEARCH TABLE users USING INTEGER PRIMARY KEY (rowid=?) (~1 rows)
+        #   0|1|1|SCAN TABLE posts (~100000 rows)
+        #
+        def pp(result) # :nodoc:
+          result.rows.map do |row|
+            row.join('|')
+          end.join("\n") + "\n"
+        end
+      end
+
       def exec_query(sql, name = nil, binds = [])
         log(sql, name, binds) do