Java 发出事先准备好的声明

在以下代码中：

PreparedStatement statement = conn
                .prepareStatement(SQLQueries.isMuted);
        statement.setString(1, player);
        statement.setString(2, player);
//in SQLQueries.java
public static final String isMuted = "SELECT EXISTS(SELECT * FROM "
        + "(SELECT playerid FROM mute, players AS player "
        + "WHERE player.username = '?' AND playerid = player.id"
        + "UNION ALL "
        + "SELECT playerid FROM tempmute, players AS player "
        + "WHERE player.username = '?' AND playerid = player.id) AS tbl) "
        + "AS isMuted;";

我得到以下错误：

[08:10:38 WARN]: java.sql.SQLException: Parameter index out of range (1 > number of parameters, which is 0).

我对此感到非常困惑，因为文档告诉我参数索引从1开始，这已经得到确认，因为当我分别将setString语句更改为0和1时，它给了我另一个错误。另外，该语句有两个占位符，所以我不理解为什么这段代码失败

---

我是否忽略了文档中的某些内容？

您需要在

player.id

后面留一个空格：

public static final String isBanned = "SELECT EXISTS(SELECT * FROM "
        + "(SELECT playerid FROM bans, players AS player "
        + "WHERE player.username = '?' AND playerid = player.id "
---------------------------------------------------------------^
        + "UNION ALL "
        + "SELECT playerid FROM tempban, players AS player "
        + "WHERE player.username = '?' AND playerid = player.id) AS tbl) "
        + "AS isBanned;";

---

可能还有其他问题。

删除

？

PreparedStatement占位符周围的引号。JDBC驱动程序将为您引用字符串。当您自己引用字符串占位符时，JDBC驱动程序认为您希望在语句中传递一个文本

？

---

您没有提到您正在使用的数据库，但是MySQL JDBC驱动程序的主要作者在这里确认了这一点：

也许您将参数添加到了

sqlquerys.ismute

而不是

isbanked

？您不应该删除参数周围的引号吗？我认为Keppil是正确的-Java在SQL中没有看到任何参数，它看到（并且不关心）一个条件检查是否与只包含一个问号的文本字符串相等。所以用？更改“？”。我添加了一个空格，但似乎无法修复它。