java - 在嵌套的sql语句java中连接动态值

Question

我尝试查找有关它的信息，但似乎没有关于它的示例。
我有这条线：

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 Eclipse 将“userID”读取为字符串，而不是变量。如何让 Eclipse 将“userID”读取为变量？

Answer 1

最佳实践是使用PreparedStatement和 placeholder 输入参数?。

示例用法（来自 JavaDocs）：

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

将该示例应用到您的案例中，您会得到如下信息：

// 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);

Answer 2

尝试这个：：

long userID = user.getId();
StringBuilder queryBuilder = new StringBuilder("select userclient.username from twitter_content.userclient where userclient.userid =");
queryBuilder.append("(select follower.followerid from twitter_content.follower where follower.followerid = userclient.userid and follower.userid = ?)");
PreparedStatement stmt = con.prepareStatement(queryBuilder.toString());
stmt.setInt(1, userId);