5

如果没有硬编码值,我将如何编写这个 sql 语句?

resultSet = statement
    .executeQuery("select * from myDatabase.myTable where name = 'john'");
// this works

而是有类似的东西:

String name = "john"; 
resultSet = statement
    .executeQuery("select * from myDatabase.myTable where name =" + name);
// Unknown column 'john' in 'where clause' at
// sun.reflect.NativeConstructorAccessorImpl.newInstance0...etc...

提前致谢..

4

6 回答 6

25

以目前的方式构建 SQL 查询是一个糟糕的主意,因为它为各种 SQL 注入攻击打开了大门。要正确执行此操作,您必须改用准备好的语句。这也将解决您目前显然遇到的各种逃避问题。

PreparedStatement statement = connection.prepareStatement("select * from myDatabase.myTable where name = ?");    
statement.setString(1, name);    
ResultSet resultSet = statement.executeQuery();

请注意,这prepareStatement()是一个昂贵的调用(除非您的应用程序服务器使用语句缓存和其他类似设施)。从理论上讲,最好只准备一次语句,然后多次重用它(尽管不是同时):

String[] names = new String[] {"Isaac", "Hello"};
PreparedStatement statement = connection.prepareStatement("select * from myDatabase.myTable where name = ?");

for (String name: names) {
    statement.setString(1, name);    
    ResultSet resultSet = statement.executeQuery();
    ...
    ...
    statement.clearParameters();
}
于 2013-01-28T15:18:46.793 回答
4

您缺少字符串周围的单引号,您的代码已更正:

String name = "john";
String sql = "select * from myDatabase.myTable where name = '" + name + "'";
// Examine the text of the query in the debugger, log it or print it out using System.out.println
resultSet = statement.executeQuery(sql);

在执行查询之前打印/记录查询的文本以查看它是否正常。

如果你要做很多类似的查询,只有常量发生变化,考虑使用准备好的语句

于 2013-01-28T15:19:07.190 回答
1

这应该工作:

String name = "john"; 
resultSet = statement
    .executeQuery("select * from myDatabase.myTable where name =" + "'" + name + "'");
于 2013-01-28T16:50:07.147 回答
0

您需要在值周围加上引号('john' 而不是 john)...

于 2013-01-28T15:18:01.253 回答
0

尝试以下操作:

String name = "john"; 

resultSet = statement
      .executeQuery("select * from myDatabase.myTable where myTable.name = '" + name + "'");
于 2013-01-28T15:26:29.143 回答
-1

name因为它是一个字符串,所以在您的值周围加上引号。

"select * from myDatabase.myTable where name ='" + name + "'"
于 2013-01-28T15:18:51.450 回答