题目
查询同一学生两次考试日期相差恰好 2 天的记录。
知识点：自连接、日期间隔
运行环境：本站提供 SQLite 环境，下面脚本可直接运行。若使用 MySQL，见文中对照；有差异的题目会同时给出 MySQL 写法。
思路
同一学生两次考试，日期相差恰好 2 天。成绩表自连接，学号相同，再用日期间隔过滤。
SQLite 没有 DATEDIFF，用儒略日相减：JULIANDAY(后) - JULIANDAY(前) = 2。
MySQL 与 SQLite 对照
| 场景 | MySQL | SQLite |
|---|---|---|
| 日期间隔天数 | DATEDIFF(sold_on, joined_on) | CAST(JULIANDAY(sold_on) - JULIANDAY(joined_on) AS INT) |
| 年龄（整岁） | TIMESTAMPDIFF(YEAR, birthday, '2025-03-12') | CAST(STRFTIME('%Y', '2025-03-12') AS INT) - CAST(STRFTIME('%Y', birthday) AS INT) - CASE WHEN STRFTIME('%m-%d', '2025-03-12') < STRFTIME('%m-%d', birthday) THEN 1 ELSE 0 END |
SQLite 解法
-- 第39题：查询考试日相邻恰好 2 天的成绩对
-- 样例数据：学生选课 + 员工部门。最后一条 SELECT 为本题查询。
DROP TABLE IF EXISTS score;
DROP TABLE IF EXISTS course;
DROP TABLE IF EXISTS student;
DROP TABLE IF EXISTS teacher;
DROP TABLE IF EXISTS emp;
DROP TABLE IF EXISTS dept;
CREATE TABLE teacher (
tid TEXT PRIMARY KEY,
tname TEXT NOT NULL
);
CREATE TABLE student (
sid TEXT PRIMARY KEY,
sname TEXT NOT NULL,
ssex TEXT,
birthday TEXT,
city TEXT,
email TEXT
);
CREATE TABLE course (
cid TEXT PRIMARY KEY,
cname TEXT NOT NULL,
tid TEXT,
credit INTEGER
);
CREATE TABLE score (
sid TEXT,
cid TEXT,
score REAL,
exam_on TEXT
);
CREATE TABLE dept (
did TEXT PRIMARY KEY,
dname TEXT NOT NULL
);
CREATE TABLE emp (
eid TEXT PRIMARY KEY,
ename TEXT NOT NULL,
did TEXT,
manager_id TEXT,
salary INTEGER,
hired_on TEXT
);
INSERT INTO teacher(tid, tname) VALUES
('T01', '何启明'),
('T02', '陆知秋'),
('T03', '裴南'),
('T04', '江衡');
INSERT INTO student(sid, sname, ssex, birthday, city, email) VALUES
('S01', '林晓', '女', '2003-03-12', '杭州', 'linxiao@campus.test'),
('S02', '周衡', '男', '2002-11-08', '宁波', 'zhouheng@campus.test'),
('S03', '沈予', '女', '2003-06-21', '杭州', 'shenyu@campus.test'),
('S04', '韩牧', '男', '2002-07-09', '温州', 'hanmu@campus.test'),
('S05', '叶安', '女', '2004-01-30', '杭州', 'yean@campus.test'),
('S06', '方迟', '男', '2001-12-19', '嘉兴', 'fangchi@campus.test'),
('S07', '苏晚', '女', '2003-09-04', '宁波', 'suwan@campus.test'),
('S08', '程远', '男', '2004-05-17', '杭州', 'chengyuan@campus.test'),
('S09', '顾星', '女', '2002-10-28', '绍兴', 'guxing@campus.test'),
('S10', '梁野', '男', '2001-02-08', '温州', 'liangye@campus.test'),
('S11', '夏禾', '女', '2003-08-16', '杭州', 'xiahe@campus.test'),
('S12', '许川', '男', '2002-04-25', '宁波', 'xuchuan@campus.test'),
('S13', '丁南', '女', '2004-04-18', '杭州', 'dingnan@campus.test'),
('S14', '蔡河', '男', '2001-06-03', '嘉兴', 'caihe@campus.test'),
('S15', '闻青', '女', '2002-08-22', '绍兴', 'wenqing@campus.test'),
('S16', '邱石', '男', '2003-12-01', '宁波', 'qiushi@campus.test');
INSERT INTO course(cid, cname, tid, credit) VALUES
('C01', '数据库原理', 'T02', 4),
('C02', '离散数学', 'T01', 3),
('C03', '操作系统', 'T03', 4),
('C04', '计算机网络', 'T02', 3),
('C05', '编译原理', 'T01', 4),
('C06', '线性代数', 'T03', 3),
('C07', '软件工程', 'T04', 2),
('C08', '人工智能', 'T04', 3),
('C09', '毕业实习', 'T03', 1);
INSERT INTO score(sid, cid, score, exam_on) VALUES
('S01', 'C01', 88, '2025-01-08'),
('S01', 'C02', 76, '2025-01-10'),
('S01', 'C03', 91, '2025-01-12'),
('S01', 'C04', 85, '2025-01-09'),
('S01', 'C05', 72, '2025-01-11'),
('S01', 'C06', 90, '2025-01-13'),
('S01', 'C07', 68, '2025-01-08'),
('S01', 'C08', 80, '2025-02-15'),
('S02', 'C01', 70, '2025-01-08'),
('S02', 'C02', 82, '2025-01-10'),
('S02', 'C03', 64, '2025-01-12'),
('S02', 'C04', 55, '2025-01-09'),
('S03', 'C01', 90, '2025-01-08'),
('S03', 'C02', 90, '2025-01-10'),
('S03', 'C03', 85, '2025-01-12'),
('S03', 'C05', 78, '2025-01-11'),
('S04', 'C01', 45, '2025-01-08'),
('S04', 'C02', 52, '2025-01-10'),
('S04', 'C03', 40, '2025-01-12'),
('S04', 'C04', 0, '2025-01-09'),
('S05', 'C01', 79, '2025-01-08'),
('S05', 'C02', 88, '2025-01-10'),
('S05', 'C03', 70, '2025-01-09'),
('S06', 'C01', 0, '2025-01-08'),
('S06', 'C03', 58, '2025-01-12'),
('S06', 'C06', 41, '2025-01-13'),
('S07', 'C02', 94, '2025-01-10'),
('S07', 'C03', 90, '2025-01-12'),
('S07', 'C07', 88, '2025-01-11'),
('S08', 'C01', 86, '2025-01-08'),
('S08', 'C02', 61, '2025-01-10'),
('S08', 'C03', 73, '2025-01-12'),
('S08', 'C08', 69, '2025-02-15'),
('S09', 'C01', 92, '2025-01-08'),
('S09', 'C03', 81, '2025-01-12'),
('S09', 'C04', 77, '2025-01-09'),
('S10', 'C02', 55, '2025-01-10'),
('S10', 'C03', 47, '2025-01-12'),
('S11', 'C01', 77, '2025-01-08'),
('S11', 'C02', 80, '2025-01-10'),
('S11', 'C03', 79, '2025-01-12'),
('S11', 'C05', 66, '2025-01-11'),
('S12', 'C01', 60, '2025-01-08'),
('S13', 'C02', 84, '2025-01-10'),
('S13', 'C07', 91, '2025-01-11'),
('S14', 'C01', 58, '2025-01-08'),
('S14', 'C06', 73, '2025-01-13'),
('S15', 'C03', 62, '2025-01-12'),
('S15', 'C08', 0, '2025-02-15');
INSERT INTO dept(did, dname) VALUES
('D01', '研发部'),
('D02', '教学部'),
('D03', '市场部');
INSERT INTO emp(eid, ename, did, manager_id, salary, hired_on) VALUES
('E01', '陈省', 'D01', NULL, 18000, '2020-03-01'),
('E02', '吴舟', 'D01', 'E01', 12000, '2022-05-12'),
('E03', '唐宁', 'D01', 'E01', 19000, '2021-08-20'),
('E04', '沈泊', 'D02', 'E01', 15000, '2021-11-04'),
('E05', '齐末', 'D02', 'E04', 9000, '2024-04-01'),
('E06', '米白', 'D03', 'E01', 11000, '2023-02-18'),
('E07', '蓝秋', 'D03', 'E06', 8000, '2024-09-01'),
('E08', '贺川', 'D03', 'E06', 21000, '2022-12-10');
-- 本题查询
SELECT a.sid, a.cid AS cid_a, a.exam_on AS day_a, b.cid AS cid_b, b.exam_on AS day_b
FROM score a
JOIN score b ON a.sid = b.sid AND CAST(JULIANDAY(b.exam_on) - JULIANDAY(a.exam_on) AS INT) = 2
ORDER BY a.sid, a.exam_on;
MySQL 解法
查询部分与 SQLite 的差异如下（建表请改用 VARCHAR / DECIMAL / DATE）。
SELECT a.sid, a.cid AS cid_a, a.exam_on AS day_a, b.cid AS cid_b, b.exam_on AS day_b
FROM score a
JOIN score b ON a.sid = b.sid AND DATEDIFF(b.exam_on, a.exam_on) = 2
ORDER BY a.sid, a.exam_on;运行示例
sid | cid_a | day_a | cid_b | day_b
----+-------+------------+-------+-----------
S01 | C01 | 2025-01-08 | C02 | 2025-01-10
S01 | C07 | 2025-01-08 | C02 | 2025-01-10
S01 | C04 | 2025-01-09 | C05 | 2025-01-11
S01 | C02 | 2025-01-10 | C03 | 2025-01-12
S01 | C05 | 2025-01-11 | C06 | 2025-01-13
S02 | C01 | 2025-01-08 | C02 | 2025-01-10
S02 | C02 | 2025-01-10 | C03 | 2025-01-12
S03 | C01 | 2025-01-08 | C02 | 2025-01-10
S03 | C02 | 2025-01-10 | C03 | 2025-01-12
S04 | C01 | 2025-01-08 | C02 | 2025-01-10
S04 | C02 | 2025-01-10 | C03 | 2025-01-12
S05 | C01 | 2025-01-08 | C02 | 2025-01-10
S07 | C02 | 2025-01-10 | C03 | 2025-01-12
S08 | C01 | 2025-01-08 | C02 | 2025-01-10
S08 | C02 | 2025-01-10 | C03 | 2025-01-12
S10 | C02 | 2025-01-10 | C03 | 2025-01-12
S11 | C01 | 2025-01-08 | C02 | 2025-01-10
S11 | C02 | 2025-01-10 | C03 | 2025-01-12