使用count sql查询在Java程序中给出“无效的列名”错误

Question

How can i use this sql query in Java Program.

String SelectSQL = "SELECT (CASE WHEN cnt >= 1
                             THEN 'True'
                             ELSE 'False'
                             END) result_str
                 FROM ( SELECT COUNT(*) cnt FROM event WHERE externaleventid ='1256294' )";

I am using Preparatory statement to pass the externaleventid. Other query works fine when I am using column name but when I don't use column name I am getting the error "Invalid column name" When I run this query in SQL developer it executes successfully.

Added java code:

String query = " SELECT (CASE WHEN COUNT(*) >= 1 THEN 'True' ELSE 'False' END) AS result_str FROM event WHERE externaleventid = ?";
PreparedStatement pstmt = conn.prepareStatement(query);
pstmt.setString(1,"1256294");
ResultSet rs = pstmt.executeQuery();
while (rs.next()) { 
    String externaleventid = rs.getString("DISPLAYNAME");
    System.out.println("externaleventid : " + externaleventid);
}

Answer 1

You should write

         "SELECT (CASE WHEN cnt >= 1
                         THEN 'True'
                         ELSE 'False'
                         END) AS result_str
             FROM ( SELECT COUNT(*) AS cnt FROM event WHERE externaleventid ='1256294' )";

instead of

        "SELECT (CASE WHEN cnt >= 1
                         THEN 'True'
                         ELSE 'False'
                         END) result_str
             FROM ( SELECT COUNT(*) cnt FROM event WHERE externaleventid ='1256294' )"; 

Answer 2

You are trying to get the result from a column named DISPLAYNAME which does not exist in your query. One option is to ignore the name and retrieve by index:

rs.getString(1);

Another is to retrieve by name, but use the name of the alias that was on the query:

rs.getString("result_str");