postgresql 在此 ResultSet 中找不到列名...
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The column name ... was not found in this ResultSet
提问by rootser
We are using java jdk 1.7.0_45, postgresql jdbc connector postgresql-9.3-1100.jdbc41.jar.
我们使用的是 java jdk 1.7.0_45，postgresql jdbc 连接器 postgresql-9.3-1100.jdbc41.jar。
Here is a synopsis of our problem, as much as possible of code pasted below.
这是我们问题的概要，尽可能多地粘贴下面的代码。
This code:
这段代码：
ResultSet rs = DbConn.getInstance().doQuery("Select d.deptId from Depts d");
while (rs.next()){
System.out.println(rs.getInt("d.deptId"));
产生错误：
org.postgresql.util.PSQLException: The column name d.deptId was not found in this ResultSet.
This code:
这段代码：
ResultSet rs = DbConn.getInstance().doQuery("Select d.deptId from Depts d");
while (rs.next()){
System.out.println(rs.getInt("deptId"));
不会产生错误。Is there a way, besides removing the "d." from the first query, to make the first code snippet notthrow the error message?
除了删除“d”之外，还有其他方法吗？从第一个查询开始，使第一个代码片段不抛出错误消息？
Here is the source code:
这是源代码：
public class JoinTest {
@Test
public void test(){
boolean pass = false;
try {
ResultSet rs = DbConn.getInstance().doQuery("Select d.deptId from Depts d");
String label = rs.getMetaData().getColumnLabel(1); // What do you get?
System.out.println("label = " + label);
while (rs.next()){
System.out.println(rs.getInt("d.deptId"));
pass = true;
}
} catch (SQLException e) {
e.printStackTrace();
pass=false;
}
assertTrue(pass);
}
@Test
public void test2(){
boolean pass = false;
try {
ResultSet rs = DbConn.getInstance().doQuery("Select d.deptId from Depts d");
while (rs.next()){
System.out.println(rs.getInt("deptId"));
pass = true;
}
} catch (SQLException e) {
e.printStackTrace();
pass=false;
}
assertTrue(pass);
}
}
public class DbConn {
private static String url = "jdbc:postgresql://server:port/schema";
private static Properties props = new Properties(); {
props.setProperty("user","userid");
props.setProperty("password","passwprd");
}
private Connection conn;
private DbConn(){}
private static DbConn instance;
public static DbConn getInstance() throws SQLException{
if (instance == null){
instance = new DbConn();
instance.conn = DriverManager.getConnection(url, props);
}
return instance;
}
public ResultSet doQuery(String query) throws SQLException{
Logger.log("DbConn.doQuery: " + query);
Statement st = conn.createStatement();
ResultSet rs = st.executeQuery(query);
return rs;
}
}
}
回答by Craig Ringer
The query:
查询：
select d.deptId from Depts d
produces a single-column resultset with the result-alias "deptId". There is no "d.deptId" column. If you want one, you can request that as the column alias instead:
生成带有结果别名“deptId”的单列结果集。没有“d.deptId”列。如果你想要一个，你可以请求它作为列别名：
select d.deptId AS "d.deptId" from Depts d
PgJDBC can't do anything about this because it has no idea that the resultset column "deptId" is related to the "d.deptId" in the select-list. Teaching it about that would force it to understand way more about the SQL it processes than would be desirable, and lead to maintenance and performance challenges.
PgJDBC 对此无能为力，因为它不知道结果集列“deptId”与选择列表中的“d.deptId”相关。教它这一点会迫使它更多地了解它所处理的 SQL，而不是它所期望的，并导致维护和性能挑战。
回答by duffymo
The second one works - why isn't that acceptable?
第二个有效 - 为什么不能接受？
You can also do this:
你也可以这样做：
System.out.println(rs.getInt(1));
If you change the query you have to change the code, too.
如果您更改查询，您也必须更改代码。
