Question

我的代码是

CREATE DATABASE JsPracticeDb; 

/* Create tables corresponding to the problems, solutions to 
   problems, and ratings of problems or solutions */
CREATE TABLE Problems 
(
    id INT PRIMARY KEY IDENTITY(1,1) NOT NULL, 
    prompt_code VARCHAR(5000) NOT NULL,
    test_func_code VARCHAR(5000) NOT NULL,
    test_input_code VARCHAR(5000) NOT NULL,
    created DATETIME DEFAULT CURRENT_TIMESTAMP
);

CREATE TABLE Solutions  
(
   id INT PRIMARY KEY IDENTITY(1,1) NOT NULL, 
   problem_id INT NOT NULL,
   solver VARCHAR(50),
   code VARCHAR(5000),
   FOREIGN KEY (problem_id) REFERENCES Problems(id) ON DELETE CASCADE,
   created DATETIME DEFAULT CURRENT_TIMESTAMP
);

CREATE TABLE Ratings 
(
    id INT PRIMARY KEY IDENTITY(1,1) NOT NULL,
    solution_id INT NOT NULL,
    stars TINYINT NOT NULL,
    FOREIGN KEY (solution_id) REFERENCES Solutions(id) ON DELETE CASCADE
);

CREATE TABLE Comments 
(
    id INT PRIMARY KEY IDENTITY(1,1) NOT NULL,
    solution_id INT NOT NULL,
    commenter VARCHAR(50),
    comment VARCHAR(2000) NOT NULL,
    created DATETIME DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY (solution_id) REFERENCES Solutions(id) ON DELETE CASCADE
);

/* Closure Table for comment hierarchy */
CREATE TABLE CommentPaths 
(
    ancestor INT NOT NULL,
    descendant INT NOT NULL,
    PRIMARY KEY (ancestor, descendant),
    FOREIGN KEY (ancestor) REFERENCES Comments(id) ON DELETE CASCADE,
    FOREIGN KEY (descendant) REFERENCES Comments(id) ON DELETE CASCADE
);
GO

/* Create trigger for deleting all comment descendants when 
   the comment is deleted */
CREATE TRIGGER deleteDescendants ON CommentPaths
FOR DELETE
AS
    DELETE FROM Comments 
    WHERE id IN (SELECT deleted.descendant FROM deleted);

我正在

Msg 2714，Level 16，State 6，Line 5
  数据库中已经有一个名为“Problems”的对象。

Msg 8197，Level 16，State 4，Procedure deleteDescendants，Line 45
  对象“CommentPaths”不存在或对此操作无效。

作为错误。还没有一个名为Problems的对象，所以我不知道为什么会这样认为。另外，为什么说CommentPaths不存在（解析触发器时不应该存在）？

Answer 1

创建数据库后，必须使用USE切换到该数据库，否则命令将发送到当前数据库，而不是新创建的数据库。

Answer 2

它显示错误，因为在您执行脚本的数据库中存在表Problems，请尝试以下解决方案

CREATE DATABASE JsPracticeDb; 
/* Create tables corresponding to the problems, solutions to 
   problems, and ratings of problems or solutions */
GO
USE[JsPracticeDb]
Go
CREATE TABLE Problems ( 
    id INT PRIMARY KEY IDENTITY(1,1) NOT NULL, 
    prompt_code VARCHAR(5000) NOT NULL,
    test_func_code VARCHAR(5000) NOT NULL,
    test_input_code VARCHAR(5000) NOT NULL,
    created DATETIME DEFAULT CURRENT_TIMESTAMP
);
CREATE TABLE Solutions (
   id INT PRIMARY KEY IDENTITY(1,1) NOT NULL, 
   problem_id INT NOT NULL,
   solver VARCHAR(50),
   code VARCHAR(5000),
   FOREIGN KEY (problem_id) REFERENCES Problems(id) ON DELETE CASCADE,
   created DATETIME DEFAULT CURRENT_TIMESTAMP
);
CREATE TABLE Ratings (
    id INT PRIMARY KEY IDENTITY(1,1) NOT NULL,
    solution_id INT NOT NULL,
    stars TINYINT NOT NULL,
    FOREIGN KEY (solution_id) REFERENCES Solutions(id) ON DELETE CASCADE
);
CREATE TABLE Comments ( 
    id INT PRIMARY KEY IDENTITY(1,1) NOT NULL,
    solution_id INT NOT NULL,
    commenter VARCHAR(50),
    comment VARCHAR(2000) NOT NULL,
    created DATETIME DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY (solution_id) REFERENCES Solutions(id) ON DELETE CASCADE
);
/* Closure Table for comment hierarchy */
CREATE TABLE CommentPaths (
    ancestor INT NOT NULL,
    descendant INT NOT NULL,
    PRIMARY KEY (ancestor, descendant),
    FOREIGN KEY (ancestor) REFERENCES Comments(id) ON DELETE CASCADE,
    FOREIGN KEY (descendant) REFERENCES Comments(id) ON DELETE CASCADE
);
/* Create trigger for deleting all comment descendants when 
   the comment is deleted */
GO
CREATE TRIGGER deleteDescendants ON CommentPaths
FOR DELETE
AS
    DELETE FROM Comments 
    WHERE id IN (SELECT deleted.descendant FROM deleted);

这将解决您的问题。

为什么我会收到“数据库中已有一个名为...的对象”？

2 个答案: