题单链接
SQL1 插入记录(一)
INSERT INTO exam_record (uid,exam_id,start_time,submit_time,score) VALUES
(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);
SQL2 插入记录(二)
INSERT INTO exam_record_before_2021(uid, exam_id, start_time, submit_time, score)
SELECT uid, exam_id, start_time, submit_time, score
FROM exam_record
WHERE YEAR(submit_time) < '2021';
SQL3 插入记录(三)
REPLACE INTO examination_info VALUES(
NULL,9003,"SQL","hard",90,"2021-01-01 00:00:00"
)
SQL4 更新记录(一)
UPDATE examination_info
SET tag="Python"
WHERE tag="PYTHON"
SQL5 更新记录(二)
UPDATE exam_record
SET submit_time='2099-01-01 00:00:00',score=0
WHERE start_time < '2021-9-1' AND score IS NULL;
SQL6 删除记录(一)
DELETE FROM exam_record
WHERE TIMESTAMPDIFF(MINUTE,start_time,submit_time)<5 AND score<60
SQL7 删除记录(二)
DELETE FROM exam_record
WHERE submit_time IS NULL OR timestampdiff(minute,start_time,submit_time)<5
ORDER BY start_time
LIMIT 3
SQL8 删除记录(三)
truncate table exam_record
SQL9 创建一张新表
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 datetime DEFAULT CURRENT_TIMESTAMP COMMENT '注册时间'
)
SQL10 修改表
ALTER TABLE user_info ADD school VARCHAR(15) AFTER level;
ALTER TABLE user_info CHANGE job profession VARCHAR(10);
ALTER TABLE user_info MODIFY achievement int(11) DEFAULT 0;
增加列在某列之后
ALTER TABLE 增加的表格 ADD 增加列的名称 数据类型 位置(after level 在level 之后)
更换列的名称及数据类型
ALTER TABLE user_info CHANGE 原列名 修改列名 修改数据类型
更改数据类型
ALTER TABLE 表名 MODIFY 修改列名称 数据类型 默认值等
SQL11 删除表
DROP TABLE IF EXISTS exam_record_2011, exam_record_2012, exam_record_2013, exam_record_2014;
SQL12 创建索引
CREATE INDEX idx_duration ON examination_info(duration);
CREATE UNIQUE INDEX uniq_idx_exam_id ON examination_info(exam_id);
CREATE FULLTEXT INDEX full_idx_tag ON examination_info(tag);
SQL13 删除索引
DROP INDEX uniq_idx_exam_id ON examination_info;
DROP INDEX full_idx_tag ON examination_info;
SQL14 SQL类别高难度试卷得分的截断平均值
SELECT tag,difficulty,
ROUND((SUM(score)-MAX(score)-MIN(score))/(COUNT(score)-2),1) AS clip_avg_score
FROM examination_info
LEFT JOIN exam_record ON examination_info.exam_id=exam_record.exam_id
WHERE tag='SQL' AND difficulty='hard';
SQL15 统计作答次数
SELECT COUNT(exam_id) AS total_pv,
COUNT(submit_time) AS complete_pv,
COUNT(DISTINCT IF(submit_time is not NULL,exam_id,null)) AS complete_exam_cnt
FROM exam_record
SQL16 得分不小于平均分的最低分
SELECT MIN(score) AS min_score_over_avg
FROM exam_record
JOIN examination_info ON examination_info.exam_id=exam_record.exam_id
WHERE examination_info.tag="SQL" AND score>=
(
SELECT avg(score) FROM exam_record
JOIN examination_info ON examination_info.exam_id=exam_record.exam_id
WHERE examination_info.tag="SQL"
)
SQL17 平均活跃天数和月活人数
SELECT DATE_FORMAT(start_time,"%Y%m") AS month,
ROUND(COUNT(distinct uid,DATE_FORMAT(start_time,"%Y%m%d")) / COUNT(distinct uid) , 2) AS avg_active_days ,
COUNT(distinct uid) AS mau
FROM exam_record
WHERE submit_time is not NULL AND YEAR(submit_time) = 2021
GROUP BY month;