1.条件判断 方式一： if ... then ... elsif ... then ... else ... end if;
方式二：
case ... when ... then ... end;
2.循环结构
方式一：
loop ... exit when ... end loop;
方式二:
wh...
1.sql语句查询顺序
select ...
from ...
where ...
group by ...
having ...
order by ...
sql语句执行顺序
from
where
group by
having
select
over
distinct
top
order by
注意：1.如果引用不在group by列表中出...
