出差管理系统的数据库表sql语句

以下是一个可能的出差管理系统的数据库表SQL语句示例。请注意，这只是一个示例，实际系统的数据库结构将根据特定的需求而有所不同。

CREATE TABLE users (
id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
username VARCHAR(255) NOT NULL,
password VARCHAR(255) NOT NULL,
email VARCHAR(255) NOT NULL,
department VARCHAR(255) NOT NULL
);

CREATE TABLE trips (
id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
user_id INT NOT NULL,
destination VARCHAR(255) NOT NULL,
start_date DATE NOT NULL,
end_date DATE NOT NULL,
purpose TEXT,
status VARCHAR(255) NOT NULL,
FOREIGN KEY (user_id) REFERENCES users(id)
);

CREATE TABLE approvals (
id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
trip_id INT NOT NULL,
approver_id INT NOT NULL,
status VARCHAR(255) NOT NULL,
comments TEXT,
FOREIGN KEY (trip_id) REFERENCES trips(id),
FOREIGN KEY (approver_id) REFERENCES users(id)
);

CREATE TABLE expenses (
id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
trip_id INT NOT NULL,
amount DECIMAL(10, 2) NOT NULL,
description TEXT,
FOREIGN KEY (trip_id) REFERENCES trips(id)
);

CREATE TABLE notifications (
id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
user_id INT NOT NULL,
message TEXT NOT NULL,
status VARCHAR(255) NOT NULL,
FOREIGN KEY (user_id) REFERENCES users(id)
);