有没有办法从已删除的记录中获取密钥？

Question

我正在使用 PostgreSQL 将表单保存在三个表中，一个用于名称和 id，另一个用于填充字段，第三个用于存储字段的值。

private static final String REMOVE_FORM = "DELETE FROM forms WHERE name = ?";
private PreparedStatement removeFormQuery;

public boolean connect() throws SQLException{
    this.connection = DriverManager.getConnection(URL);
    this.removeFormQuery = this.connection.prepareStatement(REMOVE_FORM);
}
public void close() throws SQLException {
    if(null != this.connection) {
        this.connection.close();
    }
    if(null != this.removeFormQuery) {
            this.removeFormQuery.close();
    }
}

private void removeForm(String form) {
    try {
        removeFormQuery.setString(1, form);
        int execute = removeFormQuery.executeUpdate();
        System.out.println(execute);
        ResultSet generatedKeys = removeFormQuery.getGeneratedKeys();
        while (generatedKeys.next()) {
            int anInt1 = generatedKeys.getInt("id");
            removeFieldQuery.setInt(1, anInt1);
            if (removeFieldQuery.execute())
                System.out.println("remove field failed");
            else
                System.out.println("remove field success");
            ResultSet generatedFieldsKeys = removeFieldQuery.getGeneratedKeys();
            while (generatedFieldsKeys.next()) {
                int anInt = generatedFieldsKeys.getInt("id");
                removeListItemQuery.setInt(1, anInt);
                if (removeListItemQuery.execute())
                    System.out.println("remove listItem failed");
                else
                    System.out.println("remove listItem success");
            }
        }
    } catch (SQLException e) {
        e.printStackTrace();
    }
}

执行删除查询后代码没有生成键，我错过了什么吗？

Answer 1

虽然您没有告诉我们您正在运行什么查询，但如果它们是 deletes，那么您不会期望任何生成的密钥。

来自Statement.getGeneratedKeys() 的 Javadoc：

     * Retrieves any auto-generated keys created as a result of executing this
     * Statement object. If this Statement object did
     * not generate any keys, an empty ResultSet
     * object is returned.

当您插入表时可能会自动生成键，创建需要主键的新行，但是当您删除行时不会生成键。