Oracle插入数据库之前先判断是否存在的SQL简单示例

插入语句时判断是否存在的SQL语句：

insert into appointmen_record(
   app_type_id,
   app_time_id,
   create_user,
   appointmen_date
 )
select
   "2c8f50808c3b49b1a9dda467aea1d475",
   "f982f0af7db54a87ba8f3ce189a6e66f",
   "55aaec489ea9458b99c920828c53755a",
   "2016-06-16"
from dual
   where not exists
      (select * from appointmen_record
          where appointmen_date = '2016-06-18')