mysql学习打卡day16

今日成果：

select c.customer_id,c.first_name,c.points, 'Bronze' as type
 from customers c
 where c.points < 2000
 union
 select c.customer_id,c.first_name,c.points, 'Silver' as type
 from customers c
 where c.points between 2000 and 3000
union
 select c.customer_id,c.first_name,c.points, 'Gold' as type
 from customers c
 where c.points > 3000
 order by first_name;
 -- union:用来合并多个表的查询结果，每个表的列数量需要保持一致否则会报错。

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