在嵌套的sql语句java中连接动态值

Question

我试着寻找有关它的信息，但似乎没有关于它的例子
我有这样一句话：

long userID = user.getId();
String query = "select userclient.username from twitter_content.userclient where userclient.userid = " +
            "(select follower.followerid from twitter_content.follower where follower.followerid = userclient.userid and follower.userid = "+userID+")";

但是Eclipse将“userID”读取为字符串，而不是变量。如何使Eclipse将“userID”作为变量读取

Answer 1

最佳实践是使用PreparedStatement和占位符?的输入参数

用法示例（来自JavaDocs）：

PreparedStatement stmt = con.prepareStatement("UPDATE EMPLOYEES SET SALARY = ? WHERE ID = ?");
stmt.setBigDecimal(1, 153833.00)
stmt.setInt(2, 110592)

将这个例子应用到你的案例中，你会得到如下结果：

// prepare connection "conn" earlier
long userID = user.getId();
PreparedStatement stmt = conn.prepareStatement("select userclient.username from twitter_content.userclient where userclient.userid = (select follower.followerid from twitter_content.follower where follower.followerid = userclient.userid and follower.userid = ?)");
stmt.setLong(1, userID);