java SELECT * WHERE 在 H2 数据库中
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SELECT * WHERE in H2 database
提问by salamanka44
I'm trying to do in my program a JDBC connection with my Embedded H2 database. The problem is that I couldn't execute a simple query with "WHERE ID =". In my databse, the ID are string not integer ('D58BE' in my example).
我试图在我的程序中与我的嵌入式 H2 数据库建立 JDBC 连接。问题是我无法执行带有“WHERE ID =”的简单查询。在我的数据库中,ID 是字符串而不是整数(在我的示例中为“D58BE”)。
There is my code :
有我的代码:
public Milestone findbyId(String id) throws ClassNotFoundException, SQLException {
Class.forName("org.h2.Driver");
Connection connection = DriverManager.getConnection("jdbc:h2:~/dao_db", "sa", "");
PreparedStatement prepareStatement = connection.prepareStatement("SELECT * FROM MILESTONE WHERE ID= 'D58BE'");
The problem is that the SAME query ("SELECT * FROM MILESTONE WHERE ID= 'D58BE'") works perfectly in my embeded database (I verify the result with the h2.jar provided to manage the database). While in eclipse, I had this exception :
问题是 SAME 查询(“SELECT * FROM MILESTONE WHERE ID = 'D58BE'”)在我的嵌入式数据库中完美运行(我使用为管理数据库提供的 h2.jar 验证结果)。在 eclipse 中,我有这个例外:
Exception in thread "main" org.h2.jdbc.JdbcSQLException: Column "D58BE" not found [42122-191]
I tried A LOT of things but it still never works...
我尝试了很多东西,但它仍然不起作用......
回答by Willy du Preez
To execute it directly, create a statement and execute your SQL:
要直接执行它,请创建一个语句并执行您的 SQL:
Statement statement = connection.createStatement();
statement.executeQuery("SELECT * FROM MILESTONE WHERE ID= 'D58BE'");
You are using a prepared statement, so you need to use placeholders:
您正在使用准备好的语句,因此您需要使用占位符:
PreparedStatement statement = connection.prepareStatement("SELECT * FROM MILESTONE WHERE ID=?);
statement.setString(1, "D58BE");
statement.executeQuery();
EDIT
编辑
For a detailed example and also how to process a ResultSet, you can look at the following tutorial: https://docs.oracle.com/javase/tutorial/jdbc/basics/processingsqlstatements.html
有关详细示例以及如何处理 ResultSet,您可以查看以下教程:https: //docs.oracle.com/javase/tutorial/jdbc/basics/processingsqlstatements.html
For your case it should be something along the lines of:
对于您的情况,它应该是以下内容:
ResultSet rs = stmt.executeQuery();
while (rs.next()) {
String id = rs.getString("ID");
String name = rs.getNamex("NAME"); // Assuming there is a column called name.
System.out.println(id);
}