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简介 select user.id, user.name,t.grade_sum from ( select user_id,sum(grade_num) as grade_sum from grade_info group by user_id having grade_sum = ( selec 阅读全文
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简介 联表查询, 相当于 inner join? 不是 因为不能用on select a.id, a.number, count(distinct b.number) as t_rank from passing_number as a, passing_number as b where a.nu 阅读全文
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简介 第二个select一定要起一个别名,否则会出错 注意子查询 select a.id, a.job, a.score from grade as a left join ( select job, avg(c.score) as score from grade as c group by c. 阅读全文
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简介 select user_id from ( select id, user_id, product_name, status, client_id, date, count(1) over (partition by user_id) as num from order_info where 阅读全文
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简介 select id, user_id, product_name, status, client_id, date from ( select id, user_id, product_name, status, client_id, date, count(1) over (partitio 阅读全文
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简介 from 接 子查询 count(1) 统计个数 over (partition by user_id) 以user_id 进行分区 left join on 后面还可以加上where select a.id, a.is_group_buy, b.name as client_name fro 阅读全文
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简介 考察DATE_FORMAT 与 group 联立 order by 联立 select job, DATE_FORMAT(date, '%Y-%m') as mon, sum(num) as cnt from resume_info where date like '2025%' group 阅读全文
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简介 考察 over 从一行到另一行?? 先暂时这么记忆吧 select grade, sum(number) over(order by grade) t_rank from class_grade order by grade; 阅读全文
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简介 select concat(last_name, ' ', first_name) as Name from employees; 阅读全文
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简介 INSERT INTO actor values (1, 'PENELOPE', 'GUINESS', '2006-02-15 12:34:33'), (2, 'NICK', 'WAHLBERG', '2006-02-15 12:34:33') 阅读全文
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简介 删除emp_no重复的记录，只保留最小的id对应的记录。 DELETE FROM titles_test where id not in( select * from( select MIN(id) from titles_test group by emp_no )as a ) 阅读全文
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简介 修改数据 update titles_test set emp_no = replace(emp_no, 10001, 10005) where id = 5; update titles_test set to_date = NULL, from_date ='2001-01-01' whe 阅读全文
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简介 alter table titles_test rename to titles_2017; 阅读全文
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简介 having 的使用考察 select number from grade group by number having count(number) >= 3; 阅读全文
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简介 left join select a.id, a.name, b.content from person as a left join task as b on b.person_id = a.id order by a.id; 阅读全文
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简介 简单 select user_id, max(date) from login group by user_id order by user_id; 阅读全文
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简介 使用 round 与 avg select job, round(avg(score),3) as avg from grade group by job order by avg desc; 阅读全文
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简介 使用 多个 and 并列 select * from order_info where date > "2025-10-15" and status = "completed" and product_name in("C++","Java","Python") order by id; 阅读全文
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简介 select job, sum(num) as cnt from resume_info where resume_info.date < '2026-01-01' and resume_info.date >= '2025-01-01' group by job order by cnt d 阅读全文
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简介 order by 然后 limit select * from employees order by hire_date desc limit 1; 阅读全文