Oracle 高级查询

1. 随机返回 5 条记录 

Select * from (select ename,job from emp order by dbms_random.value()) where rownum<=5 

 

 

2、处理空值排序 

select * from emp order by comm desc nulls last(first); 

 

 

3、查询跳过表中的偶数行 

select ename from (select row_number() over (order by ename) rn,ename 

from emp) x where mod(rn,2)=1; 

 

 

4.查询某用户下所有表 

select table_name from all_tables where owner='SCOTT'; 

 

 

5、查询 EMP 表中所有字段（列） 

select * from all_tab_columns where table_name='EMP'; 

 

 

6、列出表的索引列 

select * from sys.all_ind_columns where table_name='EMP'; 

select * from sys.all_ind_columns where 

upper(table_name)='CAREUSERHAM'; 

 

7、列出表中约束 

select * from all_constraints where table_name='EMP' 

 

8、在 oracle中描述数据字典视图 

select table_name ,comments from dictionary where table_name like '%TABLE%';