SQL 第55题：查询学生邮箱域名

题目

查询学生姓名及邮箱 @ 之后的域名。

知识点：SUBSTR、INSTR

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

域名是 @ 后面那一段。先用 INSTR 找到 @ 的位置，再用 SUBSTR 从后一个字符截到末尾。

MySQL 里更省事的是 SUBSTRING_INDEX(email, '@', -1)。样例邮箱都是 campus.test。

MySQL 与 SQLite 对照

SQLite 解法

-- 第55题：查询学生邮箱域名
-- 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 sname, SUBSTR(email, INSTR(email, '@') + 1) AS domain FROM student ORDER BY sid;

MySQL 解法

查询部分与 SQLite 的差异如下（建表请改用 VARCHAR / DECIMAL / DATE）。

SELECT sname, SUBSTRING_INDEX(email, '@', -1) AS domain FROM student ORDER BY sid;

运行示例

sname | domain     
------+------------
林晓    | campus.test
周衡    | campus.test
沈予    | campus.test
韩牧    | campus.test
叶安    | campus.test
方迟    | campus.test
苏晚    | campus.test
程远    | campus.test
顾星    | campus.test
梁野    | campus.test
夏禾    | campus.test
许川    | campus.test
丁南    | campus.test
蔡河    | campus.test
闻青    | campus.test
邱石    | campus.test