Tested and working.
-- Add aura to Zul'Drak Gateway Trigger if aura not present
SET @ENTRY := 28181;
SET @SPELL := 50795;
UPDATE `creature_template` SET `AIName`='SmartAI' WHERE `entry`=@ENTRY;
DELETE FROM `smart_scripts` WHERE `source_type`=0 AND `entryorguid`=@ENTRY;
INSERT INTO `smart_scripts` (`entryorguid`,`source_type`,`id`,`link`,`event_type`,`event_phase_mask`,`event_chance`,`event_flags`,`event_param1`,`event_param2`,`event_param3`,`event_param4`,`action_type`,`action_param1`,`action_param2`,`action_param3`,`action_param4`,`action_param5`,`action_param6`,`target_type`,`target_param1`,`target_param2`,`target_param3`,`target_x`,`target_y`,`target_z`,`target_o`,`comment`) VALUES
(@ENTRY,0,0,0,23,0,100,0,@SPELL,0,2000,2000,11,@SPELL,0,0,0,0,0,1,0,0,0,0,0,0,0, 'Zul''Drak Gateway Trigger - Aura Zul''Drak Gateway not present - Add Aura Zul''Drak Gateway');[/sql]