PreparedStatement使用注意

先看如下代码：

PreparedStatement pstmt = conn.prepareStatement(sql);
//执行查询
pstmt.executeQuery(sql);
//执行更新
pstmt.executeUpdate(sql);

使用上面的代码在不同数据库中分别出现错误如下：
(1)Oracle
执行查询：ORA-03115: unsupported network datatype or representation
执行更新：ORA-01008: not all variables bound
(2)MySQL

MySQL Exception: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

(3)SQLServer

SQLServer 2000 Exception: [Microsoft][SQLServer 2000 Driver for JDBC]Invalid call Statement method: {0}

原因：PreparedStatement在创建时已经缓存了sql语句，以便后面设置参数，所以你在执行查询或更新时在附加sql语句，像这样：pstmt.executeQuery(sql)，就不会设置参数，导致报错！