oracle 教材

alter session set nls_date_format='dd-mon-yyyy hh24:min:ss';
select current_date from dual;

修改 显示当前时间的格式
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对空值处理

select a,nvl(b,'为输入') from table1

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左外连接

select a.id,b.name from a ,b where a.id=b.id(+)

全部显示左边a,没有的用空值替代，不完全匹配
右外连接

select a.id,b.name from a ,b where a.id(+)=b.id

全部显示右边b

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select a ,count(a) from table where group by a having count(a)>1

查询 字段重复字段
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union  去重复
intersect  显示重复
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oracle 创建表 且数据 依赖 其他表

create  table a as select e.di ,e.name from e where e.id=001

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pl/sql

sql>set serveroutput on size 1000

sql>dbms_output.put_line('x的值'||X);

循环

begin
for i in 1..5 loop
dbms_output.put_line('i的值'||i);
end loop;
end 
/

begin
for i in  reverse 1..5 loop
dbms_output.put_line('i的值'||i);
end loop;
end 
/

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