oracle与sqlserver小结

查看所有用户 select * from all_users; select * from dba_users;select * from user_users; 查看SID select * from v$instance; 查看所有表空间 select * from v$tablespace; 查询表空间文件所在路径 select * from dba_data_files; 一：取得系统当前时间

查看所有用户

select * from all_users; 
select * from dba_users;
select * from user_users;

查看SID

select * from v$instance;

查看所有表空间

select * from v$tablespace;

select * from dba_data_files;

一：取得系统当前时间

SQLServer  select getdate();
Oracle     select sysdate from dual;

二：日期比较

SQLServer  select * from tab where Order_date > '1990-04-13';
Oracle     select * from tab where Order_date > date '1990-04-13';

三：NOt

Not逻辑运算符用来将表达式结果进行"反向"判断，以下将以比较运算符中的不等于(!=)并利用比较运算符中的等于(=)与逻辑运算符Not进行结合

select count(*) from orders where book_name != 'java基础'
select count(*) from orders where not book_name = 'java基础'

由上述SQL语法可知，当NOT逻辑运算符与比较运算符合并使用时 是将NOT置于比较运算符的前面

四：order by排序

select book_id,book_name from orders order by 1 desc,2 desc