Question

我试图让表中的第一列只是在添加新行时自动递增，而是在那里插入“ NULL ”。

以下是我插入新行的代码：

String update = "INSERT INTO help(name, area, date, message) VALUES(?, ?, ?, ?)";
    try {
        connection = plugin.getHikari().getConnection();
        // Inserting into the table
        statement = connection.prepareStatement(update);
        // Replace the '?' with the actual information
        statement.setString(1, name);
        statement.setString(2, area);
        statement.setString(3, date);
        statement.setString(4, message);
        statement.execute();
    } catch (SQLException e) {
        e.printStackTrace();
    }

以下是我创建表格的方法：

 statement = connection.prepareStatement(
                "CREATE TABLE IF NOT EXISTS help" +
                        "(" +
                        "id int," +
                        "name varchar(20)," +
                        "area varchar(25)," +
                        "date varchar(15)," +
                        "message varchar(255)" +
                        ")");
        statement.execute();

以下是每次加载/启动应用程序时运行的声明：

statement = connection.prepareStatement("ALTER TABLE help MODIFY COLUMN id INT auto_increment");

谢谢， - Nicster

Answer 1

您可以在create语句中执行所需的所有操作。问题是你的id列可以为空并且不是主键。

只需将您的创建语句更改为

即可

statement = connection.prepareStatement(
            "CREATE TABLE IF NOT EXISTS help" +
                    "(" +
                    "id int not null auto_increment," +
                    "name varchar(20)," +
                    "area varchar(25)," +
                    "date varchar(15)," +
                    "message varchar(255)" +
                    "PRIMARY KEY (id)" +
                    ")");
    statement.execute();

您不应该需要alter table语句。希望有所帮助

Answer 2

要么将主键添加到表“PRIMARY KEY（id））”这将自动增加，或者每次插入行时都必须使用java逻辑来增加值

SQL如何使第一列增量

2 个答案: