我有一个名为stars的MySQL表,其中一个字段是id_num,默认值为NULL.我想通过java中的PreparedStatement选择id_num不为NULL的所有记录.

现在我正在尝试这个：

private final String idStarsSQL = "select * from `stars` where id_num is not ?";

...

preparedStatement = (PreparedStatement) connection.prepareStatement(idStarsSQL);

preparedStatement.setString(1, NULL);

set = preparedStatement.executeQuery();

但它不起作用.

解决方法:

private final String idStarsSQL = "select * from `stars` where id_num is not NULL";

你不需要PreparedStatement.

从我的角度来看,PreparedStatement应该用于带参数的SQL语句.使用带参数的SQL语句的优点是,您可以使用相同的语句,并在每次执行时为其提供不同的值.

Statement statement = con.createStatement();

ResultSet result = statement.executeQuery("select username, age, nickname from user where nickname is not NULL");

List allUserNullNickname = new ArrayList<>();

while(result.next()){

User user = new User();

user.setUsername(result.getString("username"));

user.setAge(result.getInt("age"));

allUserNullNickname.add(user);

}

System.out.println("All user without nickname:");

allUserNullNickname.stream().forEach(user -> System.out.println("username: "+user.getUsername()+" Age: "+user.getAge()));

标签：java,mysql,select,prepared-statement,notnull,java

来源： https://codeday.me/bug/20190622/1265765.html