oracle 优化or 更换inexistsunion all几个字眼

Posted 2020-12-26 kongxc

oracle 优化or 更换in、exists、union几个字眼。测试没有问题！

根据实际情况选择相应的语句是。假设指数,or全表扫描，in 和not in 应慎用。否则会导致全表扫描。

 

 select *
   from T_Pro_Product
  where bar_code = ‘nnnmmm‘
     or name = ‘nnnmmm‘
     or no = ‘nnnmmm‘;

select *
   from T_Pro_Product
  where ‘nnnmmm‘ in (bar_code, name, no)
 
 --忧化
   select *
           from T_Pro_Product t1
          where exists
          (select 1
                   from T_Pro_Product tt1
                  where t1.bar_code = ‘nnnmmm‘
                 union all
                 select 1
                   from T_Pro_Product tt2
                  where t1.no = ‘nnnmmm‘
                 union all
                 select 1 from T_Pro_Product tt3 where t1.name like ‘n%‘)
         
         --忧化
           select *
                   from T_Pro_Product t1
                  where t1.id in (select id
                                    from T_Pro_Product tt1
                                   where t1.bar_code = ‘nnnmmm‘
                                  union all
                                  select id
                                    from T_Pro_Product tt2
                                   where t1.no = ‘nnnmmm‘
                                  union all
                                  select id
                                    from T_Pro_Product tt3
                                   where t1.name = ‘nnnmmm‘)


来源：http://www.cnblogs.com/yxwkf/p/4602143.html