fix mysql problems with boolean cast and temp tables

refs CNVS-7032

 * mysql doesn't have boolean
 * mysql will auto-commit the transaction unless you explicitly say
   TEMPORARY when dropping the temp table

Change-Id: Iaca3ddd5768f509a0b610925f601e1712e9b7d42
Reviewed-on: https://gerrit.instructure.com/22666
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>
Reviewed-by: Jacob Fugal <jacob@instructure.com>

Author: ccutrer

lib/canvas/temp_table.rb

@@ -42,7 +42,8 @@ def execute_frd
 
         yield self
       ensure
-        @connection.execute "DROP TABLE #{@name}"
+        temporary = "TEMPORARY " if @connection.adapter_name == 'Mysql2'
+        @connection.execute "DROP #{temporary}TABLE #{@name}"
       end
     end
 

lib/due_date_cacher.rb

@@ -29,12 +29,13 @@ def recompute
     shard.activate do
       Assignment.transaction do
         # create temporary table
+        cast = Submission.connection.adapter_name == 'Mysql2' ? 'UNSIGNED INTEGER' : 'BOOL'
         Assignment.connection.execute("CREATE TEMPORARY TABLE calculated_due_ats AS (#{submissions.select([
           "submissions.id AS submission_id",
           "submissions.user_id",
           "submissions.assignment_id",
           "assignments.due_at",
-          "CAST(#{Submission.sanitize(false)} AS BOOL) AS overridden"
+          "CAST(#{Submission.sanitize(false)} AS #{cast}) AS overridden"
         ]).joins(:assignment).to_sql})")
 
         # create an ActiveRecord class around that temp table for the update_all
@@ -57,7 +58,8 @@ def recompute
           update_all("cached_due_date=calculated_due_ats.due_at")
 
         # clean up
-        Assignment.connection.execute("DROP TABLE calculated_due_ats")
+        temporary = "TEMPORARY " if Assignment.connection.adapter_name == 'Mysql2'
+        Assignment.connection.execute("DROP #{temporary}TABLE calculated_due_ats")
       end
     end
   end