Oracle SQL总结

Oracle SQL总结

统计前15天日期

select
	to_char( ( sysdate - rownum + 1 ), 'yyyy-MM-dd' ) as day 
from
	user_objects 
where
	rownum < 15

查看执行计划

explain plan for select * from user_objects;
select * from table(dbms_xplan.display);

临时表

with
	temp1 as (select * from user),
	temp2 as (select * from xxx),
	temp2 as (select * from xxx)

select * from temp1,temp2,temp3;

日期格式化

select to_date('2021-03-18 22:48:06', 'yyyy-MM-dd hh24:mi:ss') from dual;
select to_char(sysdate, 'yyyy-MM-dd') from dual;

截取指定字符串

select substr('hello, world!', 0, 5) from dual;

拼接字符串

select concat('hello', ' ', 'world') as greeting from dual;