oracle 惯用sql2

oracle 常用sql2
--修改表结构
alter table t_abc modify(act default 1);
alter table t_def  add column1 type add column2 type add column3 type ... ;
alter table t_ggg drop column column_name;

alter table table_name rename column old_value to new_value;


3、修改字段

alter table table_name modify (column_name type);

--case
SELECT CASE SIGN(5 - 5)
         WHEN 1 THEN
          'Is Positive'
         WHEN -1 THEN
          'Is Negative'
         ELSE
          'Is Zero'
       END
       as accountTemp
  FROM DUAL;

--查看数据内容存储结构
select t.type, dump(t.type),dump('汉') from t_abc t;
select chr(115) from dual;
select lengthb('袁') from dual;


--在command中执行,查看表结构
desc t_abc;

-- 查询空余表空间
select 
tablespace_name,  
count(*) as extends,  
round(sum(bytes)/1024/1024, 2) as MB,  
sum(blocks) as blocks  
from dba_free_space group by tablespace_name;  

--查询各个表空间容量
select tablespace_name, sum(bytes)/1024/1024 as MB from dba_data_files group by tablespace_name;