当 www_92game_net_d_ecms_app表67472条的时候，性能对比

SELECT id FROM www_92game_net_d_ecms_app where classid ='49' or newstime ='1577808000'

OK
时间: 0.174s

SELECT id FROM www_92game_net_d_ecms_app WHERE classid = '49' UNION ALL ( SELECT id FROM www_92game_net_d_ecms_app WHERE newstime = '1577808000' )

OK
时间: 0.109s

UNION ALL 在有复杂查询的时候，性能更加优秀，小表性能差不多