SQL常见笔试题

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有一张数据表DDR

问题：查询出T2重复出现1次以上的记录

SQL Reference

select * from ddr 
where t2 in 
(
	select t2 from ddr 
	group by t2 
	having count(t2) > 1
);

 
数据库2张表，一张Customer，字段id，name；一张Orders，字段id，cid（Customer的ID外键），revenue，问题：查询出每个Customer的revenue总和

SQL Reference

select sum(revenue), c.name
from orders o LEFT JOIN customer c on o.cid = c.id 
GROUP BY cid;