sql server里怎么将varchar大于19用代码表示

在 SQL Server 中，如果你想检查 `VARCHAR` 类型的字段长度是否大于 19，你可以使用 `LEN()` 函数或 `CHARINDEX()` 函数结合条件判断来完成。以下是两种常见的做法：

1. **使用 LEN() 函数**:

   SELECT CASE WHEN LEN(your_column) > 19 THEN '长度大于19'
             ELSE '长度小于等于19'
       END AS length_status
   FROM your_table;

这段查询会返回每个记录中 `your_column` 的长度状态。

2. **使用 CHARINDEX() 函数** (如果允许有空格):

   SELECT CASE WHEN CHARINDEX(' ', your_column + ' ') > 20 THEN '长度大于19'
             ELSE '长度小于等于19'
       END AS length_status
   FROM your_table;

这里通过查找空格的数量来估算字符串长度，因为 `VARCHAR` 最大可以容纳 2^31 - 1 个字符（约 2GB），所以加上一个空格后的总长度大于 20 就意味着原始字符串长度超过 19 字符。

记得替换 `your_column` 和 `your_table` 为实际的列名和表名。

相关问题

生成sqlserver学生信息管理系统，给出注释，每个表加5条数据，需要5个表，给出完整的步骤和sql代码，并且给出10个sql问题和答案

步骤：

1. 创建数据库

CREATE DATABASE StudentInfo;

2. 创建表

CREATE TABLE Student (
    id INT PRIMARY KEY IDENTITY(1,1),
    name VARCHAR(50) NOT NULL,
    gender VARCHAR(10) NOT NULL,
    age INT NOT NULL,
    address VARCHAR(100) NOT NULL,
    phone VARCHAR(20) NOT NULL,
    email VARCHAR(50) NOT NULL
);

CREATE TABLE Course (
    id INT PRIMARY KEY IDENTITY(1,1),
    name VARCHAR(50) NOT NULL,
    credit INT NOT NULL,
    teacher VARCHAR(50) NOT NULL
);

CREATE TABLE Score (
    id INT PRIMARY KEY IDENTITY(1,1),
    student_id INT NOT NULL,
    course_id INT NOT NULL,
    score INT NOT NULL,
    FOREIGN KEY (student_id) REFERENCES Student(id),
    FOREIGN KEY (course_id) REFERENCES Course(id)
);

CREATE TABLE Class (
    id INT PRIMARY KEY IDENTITY(1,1),
    name VARCHAR(50) NOT NULL,
    teacher VARCHAR(50) NOT NULL
);

CREATE TABLE Student_Class (
    student_id INT NOT NULL,
    class_id INT NOT NULL,
    PRIMARY KEY (student_id, class_id),
    FOREIGN KEY (student_id) REFERENCES Student(id),
    FOREIGN KEY (class_id) REFERENCES Class(id)
);

3. 插入数据

INSERT INTO Student (name, gender, age, address, phone, email)
VALUES ('张三', '男', 18, '北京市朝阳区', '13811112222', 'zhangsan@qq.com'),
       ('李四', '女', 19, '北京市海淀区', '13911113333', 'lisi@qq.com'),
       ('王五', '男', 20, '北京市东城区', '15811114444', 'wangwu@qq.com'),
       ('赵六', '女', 21, '北京市西城区', '17711115555', 'zhaoliu@qq.com'),
       ('钱七', '男', 22, '北京市通州区', '18611116666', 'qianqi@qq.com');

INSERT INTO Course (name, credit, teacher)
VALUES ('语文', 4, '张老师'),
       ('数学', 4, '李老师'),
       ('英语', 4, '王老师'),
       ('物理', 3, '赵老师'),
       ('化学', 3, '钱老师');

INSERT INTO Score (student_id, course_id, score)
VALUES (1, 1, 85),
       (1, 2, 90),
       (1, 3, 88),
       (1, 4, 78),
       (1, 5, 92),
       (2, 1, 92),
       (2, 2, 87),
       (2, 3, 89),
       (2, 4, 90),
       (2, 5, 95),
       (3, 1, 80),
       (3, 2, 85),
       (3, 3, 82),
       (3, 4, 88),
       (3, 5, 90),
       (4, 1, 75),
       (4, 2, 80),
       (4, 3, 78),
       (4, 4, 82),
       (4, 5, 85),
       (5, 1, 90),
       (5, 2, 92),
       (5, 3, 88),
       (5, 4, 85),
       (5, 5, 90);

INSERT INTO Class (name, teacher)
VALUES ('高一一班', '张老师'),
       ('高一二班', '李老师'),
       ('高一三班', '王老师'),
       ('高一四班', '赵老师'),
       ('高一五班', '钱老师');

INSERT INTO Student_Class (student_id, class_id)
VALUES (1, 1),
       (2, 1),
       (3, 2),
       (4, 2),
       (5, 3);

4. SQL问题和答案

1. 查询所有学生信息

SELECT * FROM Student;

2. 查询所有课程信息

SELECT * FROM Course;

3. 查询所有成绩信息

SELECT * FROM Score;

4. 查询所有班级信息

SELECT * FROM Class;

5. 查询张三的成绩信息

SELECT * FROM Score WHERE student_id = 1;

6. 查询高一一班的学生信息

SELECT * FROM Student WHERE id IN (SELECT student_id FROM Student_Class WHERE class_id = 1);

7. 查询语文课程成绩大于90的学生信息

SELECT * FROM Student WHERE id IN (SELECT student_id FROM Score WHERE course_id = 1 AND score > 90);

8. 查询李老师教授的所有课程信息

SELECT * FROM Course WHERE teacher = '李老师';

9. 查询高一一班的所有学生的总分数

SELECT SUM(score) FROM Score WHERE student_id IN (SELECT student_id FROM Student_Class WHERE class_id = 1);

10. 查询所有学生的平均分数

SELECT AVG(score) FROM Score;

生成sqlserver学生信息管理系统，给出字段注释，需要5个表每个表加5条数据，给出完整的步骤，并且给出20个sql问题和答案

1. 创建数据库

CREATE DATABASE StudentInfo;

2. 创建表格

CREATE TABLE Student (
    StudentID INT PRIMARY KEY,
    FirstName VARCHAR(50) NOT NULL,
    LastName VARCHAR(50) NOT NULL,
    Gender CHAR(1) NOT NULL,
    DateOfBirth DATE NOT NULL,
    Email VARCHAR(50) NOT NULL,
    PhoneNumber VARCHAR(20) NOT NULL,
    Address VARCHAR(100) NOT NULL
);

CREATE TABLE Course (
    CourseID INT PRIMARY KEY,
    CourseName VARCHAR(50) NOT NULL,
    Department VARCHAR(50) NOT NULL,
    Credits INT NOT NULL
);

CREATE TABLE Enrollment (
    EnrollmentID INT PRIMARY KEY,
    StudentID INT NOT NULL,
    CourseID INT NOT NULL,
    Grade DECIMAL(3,2),
    FOREIGN KEY (StudentID) REFERENCES Student(StudentID),
    FOREIGN KEY (CourseID) REFERENCES Course(CourseID)
);

CREATE TABLE Instructor (
    InstructorID INT PRIMARY KEY,
    FirstName VARCHAR(50) NOT NULL,
    LastName VARCHAR(50) NOT NULL,
    Email VARCHAR(50) NOT NULL,
    PhoneNumber VARCHAR(20) NOT NULL,
    Department VARCHAR(50) NOT NULL
);

CREATE TABLE Department (
    DepartmentID INT PRIMARY KEY,
    DepartmentName VARCHAR(50) NOT NULL,
    Budget DECIMAL(10,2) NOT NULL,
    StartDate DATE NOT NULL,
    InstructorID INT NOT NULL,
    FOREIGN KEY (InstructorID) REFERENCES Instructor(InstructorID)
);

3. 插入数据

INSERT INTO Student (StudentID, FirstName, LastName, Gender, DateOfBirth, Email, PhoneNumber, Address) VALUES
(1, 'John', 'Doe', 'M', '1999-01-01', 'john.doe@email.com', '1234567890', '123 Main St'),
(2, 'Jane', 'Doe', 'F', '1999-01-02', 'jane.doe@email.com', '2345678901', '456 Center St'),
(3, 'Bob', 'Smith', 'M', '1999-01-03', 'bob.smith@email.com', '3456789012', '789 Pine St'),
(4, 'Sue', 'Johnson', 'F', '1999-01-04', 'sue.johnson@email.com', '4567890123', '321 Oak St'),
(5, 'Tom', 'Brown', 'M', '1999-01-05', 'tom.brown@email.com', '5678901234', '654 Birch St');

INSERT INTO Course (CourseID, CourseName, Department, Credits) VALUES
(1, 'Introduction to Computer Science', 'Computer Science', 4),
(2, 'Calculus I', 'Mathematics', 4),
(3, 'Introduction to Psychology', 'Psychology', 3),
(4, 'Introduction to Sociology', 'Sociology', 3),
(5, 'World History', 'History', 3);

INSERT INTO Enrollment (EnrollmentID, StudentID, CourseID, Grade) VALUES
(1, 1, 1, 3.7),
(2, 2, 1, 3.9),
(3, 3, 2, 3.5),
(4, 4, 3, 4.0),
(5, 5, 4, 3.8);

INSERT INTO Instructor (InstructorID, FirstName, LastName, Email, PhoneNumber, Department) VALUES
(1, 'David', 'Johnson', 'david.johnson@email.com', '1234567890', 'Computer Science'),
(2, 'Mary', 'Smith', 'mary.smith@email.com', '2345678901', 'Mathematics'),
(3, 'Susan', 'Jones', 'susan.jones@email.com', '3456789012', 'Psychology'),
(4, 'John', 'Brown', 'john.brown@email.com', '4567890123', 'Sociology'),
(5, 'Robert', 'Lee', 'robert.lee@email.com', '5678901234', 'History');

INSERT INTO Department (DepartmentID, DepartmentName, Budget, StartDate, InstructorID) VALUES
(1, 'Computer Science', 100000, '2000-01-01', 1),
(2, 'Mathematics', 80000, '2000-01-01', 2),
(3, 'Psychology', 60000, '2000-01-01', 3),
(4, 'Sociology', 50000, '2000-01-01', 4),
(5, 'History', 40000, '2000-01-01', 5);

4. SQL问题及其答案

1. 查询所有学生信息

SELECT * FROM Student;

2. 查询所有课程信息

SELECT * FROM Course;

3. 查询所有学生选修的课程和成绩

SELECT s.FirstName, s.LastName, c.CourseName, e.Grade
FROM Student s
JOIN Enrollment e ON s.StudentID = e.StudentID
JOIN Course c ON e.CourseID = c.CourseID;

4. 查询某个学生选修的所有课程和成绩

SELECT s.FirstName, s.LastName, c.CourseName, e.Grade
FROM Student s
JOIN Enrollment e ON s.StudentID = e.StudentID
JOIN Course c ON e.CourseID = c.CourseID
WHERE s.FirstName = 'John' AND s.LastName = 'Doe';

5. 查询某个课程的所有学生和成绩

SELECT s.FirstName, s.LastName, c.CourseName, e.Grade
FROM Student s
JOIN Enrollment e ON s.StudentID = e.StudentID
JOIN Course c ON e.CourseID = c.CourseID
WHERE c.CourseName = 'Introduction to Computer Science';

6. 查询成绩大于等于3.5的学生和课程信息

SELECT s.FirstName, s.LastName, c.CourseName, e.Grade
FROM Student s
JOIN Enrollment e ON s.StudentID = e.StudentID
JOIN Course c ON e.CourseID = c.CourseID
WHERE e.Grade >= 3.5;

7. 查询每个系的预算总额

SELECT d.DepartmentName, SUM(d.Budget) AS TotalBudget
FROM Department d
GROUP BY d.DepartmentName;

8. 查询选修课程最多的学生

SELECT s.FirstName, s.LastName, COUNT(e.CourseID) AS NumCourses
FROM Student s
JOIN Enrollment e ON s.StudentID = e.StudentID
GROUP BY s.FirstName, s.LastName
ORDER BY NumCourses DESC
LIMIT 1;

9. 查询任课教师是David Johnson的所有课程

SELECT c.CourseName, c.Department
FROM Course c
JOIN Instructor i ON c.Department = i.Department
WHERE i.FirstName = 'David' AND i.LastName = 'Johnson';

10. 查询选修了Introduction to Computer Science课程的所有学生

SELECT s.FirstName, s.LastName
FROM Student s
JOIN Enrollment e ON s.StudentID = e.StudentID
JOIN Course c ON e.CourseID = c.CourseID
WHERE c.CourseName = 'Introduction to Computer Science';

11. 查询选修了Calculus I课程的学生数量

SELECT COUNT(DISTINCT e.StudentID) AS NumStudents
FROM Enrollment e
JOIN Course c ON e.CourseID = c.CourseID
WHERE c.CourseName = 'Calculus I';

12. 查询选修课程数量大于等于3门的学生

SELECT s.FirstName, s.LastName, COUNT(e.CourseID) AS NumCourses
FROM Student s
JOIN Enrollment e ON s.StudentID = e.StudentID
GROUP BY s.FirstName, s.LastName
HAVING NumCourses >= 3;

13. 查询每个学生的平均成绩

SELECT s.FirstName, s.LastName, AVG(e.Grade) AS AvgGrade
FROM Student s
JOIN Enrollment e ON s.StudentID = e.StudentID
GROUP BY s.FirstName, s.LastName;

14. 查询每个系的平均预算

SELECT d.DepartmentName, AVG(d.Budget) AS AvgBudget
FROM Department d
GROUP BY d.DepartmentName;

15. 查询选修课程数量最多的学生的选修课程信息

SELECT s.FirstName, s.LastName, c.CourseName, e.Grade
FROM Student s
JOIN Enrollment e ON s.StudentID = e.StudentID
JOIN Course c ON e.CourseID = c.CourseID
WHERE s.StudentID = (
    SELECT e2.StudentID
    FROM Enrollment e2
    GROUP BY e2.StudentID
    ORDER BY COUNT(DISTINCT e2.CourseID) DESC
    LIMIT 1
);

16. 查询选修了所有课程的学生

SELECT s.FirstName, s.LastName
FROM Student s
WHERE NOT EXISTS (
    SELECT c.CourseID
    FROM Course c
    WHERE NOT EXISTS (
        SELECT e.StudentID
        FROM Enrollment e
        WHERE e.StudentID = s.StudentID AND e.CourseID = c.CourseID
    )
);

17. 查询选修了至少一门课程的学生数量

SELECT COUNT(DISTINCT e.StudentID) AS NumStudents
FROM Enrollment e;

18. 查询选修了所有课程的学生数量

SELECT COUNT(DISTINCT e.StudentID) AS NumStudents
FROM Enrollment e
WHERE NOT EXISTS (
    SELECT c.CourseID
    FROM Course c
    WHERE NOT EXISTS (
        SELECT e2.StudentID
        FROM Enrollment e2
        WHERE e2.StudentID = e.StudentID AND e2.CourseID = c.CourseID
    )
);

19. 查询选修课程最多的系

SELECT d.DepartmentName, COUNT(DISTINCT e.StudentID) AS NumStudents
FROM Department d
JOIN Instructor i ON d.InstructorID = i.InstructorID
JOIN Course c ON d.DepartmentName = c.Department
JOIN Enrollment e ON c.CourseID = e.CourseID
GROUP BY d.DepartmentName
ORDER BY NumStudents DESC
LIMIT 1;

20. 查询每个学生的选修课程数量

SELECT s.FirstName, s.LastName, COUNT(e.CourseID) AS NumCourses
FROM Student s
JOIN Enrollment e ON s.StudentID = e.StudentID
GROUP BY s.FirstName, s.LastName;