风无云的知识分享

sec@ora10g> set autotrace on sec@ora10g> select * from t where x = 'secooler'; X -------- secooler Execution Plan ---------------------------------------------------------- Plan has

检验minus差集作用：(输出1) select a from (select 1 a from dual union all  select 1 a from dual union all select 3 a from dual union all  select 4 a from dual ) t1 minus select a from (select 21 a from