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www大王叫我来巡山
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兰州文理学院
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www大王叫我来巡山
2022-06-18 11:10
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题解 | #浙大不同难度题目的正确率#
关键点知识点多表合并及计算正确率(需要流程空值函数) select difficult_level, (sum(case when question_practice_detail.result = 'right' then 1 else 0 end) / count(question_practice_detail.result)) correct_rate from user_profile inner join question_practice_detail on user_profile.device_id = question_practice_detail.device_id i...
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www大王叫我来巡山
2022-05-28 11:52
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题解 | #SQL类别高难度试卷得分的截断平均值#
必须注意聚合分数时直接avg会提示出错 select tag, difficulty, round((sum(score) - max(score) - min(score)) / (count(score) - 2), 1) as clip_avg_score from exam_record join examination_info using(exam_id) where tag="SQL" and difficulty="hard"
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www大王叫我来巡山
2022-05-14 11:59
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题解 | #创建一张新表#
level 注意用``,而不是用‘’ CREATE TABLE IF NOT EXISTS user_info_vip ( id int PRIMARY KEY AUTO_INCREMENT COMMENT '自增ID', uid int UNIQUE NOT NULL COMMENT '用户ID', nick_name varchar(64) COMMENT '昵称', achievement int DEFAULT 0 COMMENT '成就值', level int COMMENT '用户等级', job varchar(32) COMMENT '职业方向', register_time...
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www大王叫我来巡山
2022-05-14 11:05
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题解 | #删除记录(二)#
关注limit 取值 delete from exam_record where timestampdiff(minute,start_time,submit_time) < 5 or submit_time is null order by start_time limit 3
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www大王叫我来巡山
2022-05-14 10:53
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题解 | #删除记录(一)#
知识点:delete from 表名 where 删除条件 开始时间与结束时间只差 delete from exam_record where timestampdiff(minute,start_time,submit_time)<5 and score <60
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www大王叫我来巡山
2022-05-14 10:30
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题解 | #更新记录(二)#
update set 字段1=修改值,字段2=修改值... 筛选条件日期20210901之前且分数为空值(未答完) update exam_record set submit_time = '2099-01-01 00:00:00',score = 0 where start_time <'2021-09-01 00:00:00' and score is null
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www大王叫我来巡山
2022-05-14 10:09
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题解 | #更新记录(一)#
update examination_info set tag = 'Python' where tag = 'PYTHON'
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www大王叫我来巡山
2022-05-06 22:04
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题解 | #插入记录(一)#
insert into exam_record (uid, exam_id, start_time, submit_time, score)value (1001,9001,'2021-09-01 22:11:12','2021-09-01 23:01:12',90), (1002,9002,'2021-09-04 07:01:02',null,null)
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www大王叫我来巡山
2022-05-02 23:19
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题解 | #纠错4#
行连接后,再排序 SELECT cust_name, cust_contact, cust_email FROM Customers WHERE cust_state = 'MI' UNION SELECT cust_name, cust_contact, cust_email FROM Customers WHERE cust_state = 'IL'ORDER BY cust_name;
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www大王叫我来巡山
2022-05-02 23:08
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题解 | #将两个 SELECT 语句结合起来(一)#
select prod_id,quantity from OrderItems where quantity = 100 union all select prod_id,quantity from OrderItems where prod_id like "BNBG%" order by prod_id
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www大王叫我来巡山
2022-04-24 22:31
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题解 | #返回产品名称和每一项产品的总订单数#
#outer join 等于left join union right join 思路: select A.prod_name,count(A.order_num) orders from (select prod_name,order_num from Products left join OrderItems on Products.prod_id = OrderItems.prod_id union select prod_name,order_num from OrderItems right join Products on Products.prod_id = OrderItems...
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www大王叫我来巡山
2022-04-23 13:04
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题解 | #返回产品名称和与之相关的订单号#
#outer join = left join and right join select prod_name,order_num from Products left join OrderItems on Products.prod_id = OrderItems.prod_id union select prod_name,order_num from OrderItems left join Products on OrderItems.prod_id = Products.prod_id order by prod_name
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www大王叫我来巡山
2022-04-23 12:52
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题解 | #检索每个顾客的名称和所有的订单号(二)#
区分有空值左右表 select cust_name,order_num from Customers left join Orders on Orders.cust_id = Customers.cust_id order by cust_name
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www大王叫我来巡山
2022-04-23 12:33
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题解 | #确定最佳顾客的另一种方式(二)#
select Customers.cust_name, sum(OrderItems.item_price*OrderItems.quantity) total_price from Orders inner join OrderItems on Orders.order_num = OrderItems.order_num inner join Customers on Orders.cust_id = Customers.cust_id group by Customers.cust_name having total_price>=1000 order by total_price
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www大王叫我来巡山
2022-04-23 11:58
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题解 | #返回购买 prod_id 为 BR01 的产品的所有顾客的电子邮件(二)#
select cust_email from Orders inner join OrderItems on OrderItems.order_num = Orders.order_num inner join Customers on Orders.cust_id = Customers.cust_id where OrderItems.prod_id = 'BR01'
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