oracle

BITAND(nExpression1， nExpression2)
select * from table_name where bitand(nExpression1,nExpression2)= 2

查看多少张表:
select count from ALL_TABLES
select * from tabs
select * from cat
select * from all_tab_columns
select table_name from user_tables

select table_name from user_tables;
select table_name from all_tables;
select table_name from dba_tables;
查询字段
select * user_tab_columns;
select * all_tab_columns;
select * dba_tab_columns;

比较日期大小to_char
select to_char(sysdate, 'MM-DD-YYYY HH24:MI:SS') "now" from dual
select * from table_name where to_char(column_name,'yyyymmdd')>'20110427'
update table_name set column_name='xx' where column_name=851

select distinct column_name from table_name

删除数据
delete from jaysn where username='jaysn'
insert into jaysn(xx,xx) values(xx,xx)

alter table jaysn add sex varchar2(10)
alter table jaysn drop column sex

1.增加字段
alter table table_name add newColumn varchar2(200)
2.删除字段
ALTER TABLE table_name DROP COLUMN column_NAME
3.修改字段类型
alter table test modify test1 varchar2(100);
4.修改字段名
alter table test rename column test1 to test3;

5.添加主键：Alter table tabname add primary key(col)

　删除主键：Alter table tabname drop primary key(col)

6.创建索引：create [unique] index idxname on tabname(col....)
　删除索引：drop index idxname
　注：索引是不可更改的，想更改必须删除重新建。

7.创建视图：create view viewname as select statement
　删除视图：drop view viewname