preparedStatement语法错误

我最近遇到了Java PreparedStatements的这个问题。 我有以下代码：

String selectSql1 = "SELECT `value` FROM `sampling_numbers` WHERE `value` < (?)" ; ResultSet rs1 = con.select1(selectSql1,randNum); 

select1方法的位置

  public ResultSet select1(String sql, int randNum) { try { this.stmt = con.prepareStatement(sql); stmt.setInt(1, randNum); return this.stmt.executeQuery(sql); } catch (SQLException e) { e.printStackTrace(); return null; } } 

但是，它一直在抛出这个错误：

 com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '?)' at line 1 at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27) at java.lang.reflect.Constructor.newInstance(Constructor.java:513) at com.mysql.jdbc.Util.handleNewInstance(Util.java:411) at com.mysql.jdbc.Util.getInstance(Util.java:386) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1054) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4237) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4169) at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2617) at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2778) at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2828) at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2777) at com.mysql.jdbc.StatementImpl.executeQuery(StatementImpl.java:1651) at util.P_DBCon.select1(P_DBCon.java:59) at app.RandomNumberGenerator.main(RandomNumberGenerator.java:60) Exception in thread "main" java.lang.NullPointerException at app.RandomNumberGenerator.main(RandomNumberGenerator.java:64) 

当我以天真的方式做“… value < " + randNum时，这个问题不会发生，但我想这样做。

任何帮助深表感谢。

UPDATE

我尝试了社区的各种建议，比如

 String selectSql1 = "SELECT `value` FROM `sampling_numbers` WHERE value < ?" ; String selectSql1 = "SELECT value FROM sampling_numbers WHERE value < ?" ; 

仍然出现错误消息。

Answer 1

您的问题的解决方案实际上非常简单，当您要调用PreparedStatement.executeQuery（）时，您正在调用Statement.executeQuery（String ） –

 this.stmt = con.prepareStatement(sql); // Prepares the Statement. stmt.setInt(1, randNum); // Binds the parameter. // return this.stmt.executeQuery(sql); // calls Statement#executeQuery return this.stmt.executeQuery(); // calls your set-up PreparedStatement 

Answer 2

 public ResultSet select1(String sql, int randNum) { try { this.stmt = con.prepareStatement(sql); stmt.setInt(1, randNum); return this.stmt.executeQuery(); } catch (SQLException e) { e.printStackTrace(); return null; } } 

供参考，见下面的代码

 PreparedStatement statement = con.prepareStatement("SELECT EMP_ID,EMP_PWD FROM employee " + "WHERE EMP_ID = '"+param1+"'"); ResultSet result = statement.executeQuery();