select * from a union select * from b 能详细说下么

select * from a union select * from b 能详细说下么 select * into b from a where 11 select * from (select a.*,rownum aa from table a ) where aa=10 select *from A where A.a like '%1%'||'%' Please select a city or zipcode from the drop-down. Please select a plan from the options to the select * from book limit , insert into a select * from b 和select * into a from b 这两个语句是不是一样的? select id from (select id from pedigree group by number having count(name)>1)as a; 为啥用as a select c.*,d* from ( select 图号 from ( SELECT a.*,b.存货编码 FROM 未明图号 as a left OUTER JOIN 存select c.*,d* from ( select 图号 from (SELECT a.*,b.存货编码FROM 未明图号 as a left OUTER JOIN 存货档案 as bON a.图号=b.规 select from 表 和select from [表]有什么不同? select count(*) from 怎么使用 select count(1) from emp select * into dept2 from dept HQL 的语法：select a from a where a=3 or select b from b whereb=2 要怎么写? select * from tb1 a where =(select min(id2) from tb1 where id1=a.id1)其中的a该如何理解? 帮我看看这个oracle语句,select groupid,parentid,groupname,isleaf,description,sharerankid,statusid,corporationid,staffid,isactual,groupcount,level FROM (SELECT a.*,b.groupcount FROM teabgroup a,(SELECT groupid,count(*) groupcount FROM teabmembe select * from a,b与select * from a inner join b 的取数方式和执行效率有什么不同,