JDBC中SQL语句的Select子句中的游标

Question

I have a query in which I am using Cursors in Select clause along with some other columns Values.I wanted to iterate through its result via ResultSet in Java.But couldn't find a way to get the Cusror from the result set.Is it possible to do so?Can anyone help me?

For eg

select name, roll_no,
    cursor (select subj1 
        from Subject
        where id = 'abc' 
        ) as cusr1
from student

Answer 1

Here would be a generic way to read columns from a ResultSet.

    while (resultSet.next()) { //Read every row
        int columnCount = resultSet.getMetaData().getColumnCount();
        for (int column = 1; column <= columnCount; column++) { //Read every column
            String columnName = resultSet.getMetaData().getColumnName(column);
            Object value = resultSet.getObject(columnName);
            if (value != null) {
                doSomething(columnName, value);
            }

        }         
    }

Answer 2

I assume you are using an Oracle DB. I also assume Java 7 or higher (try with resources).

You are using a Cursor Expression in your SQL.

The Oracle JDBC Driver returns a java.sql.Resultset object when you call Resultset.getObject(column number|column label) for a Cursor Expression column.

So it is safe to cast:

try (Resultset innerResultset =  (Resultset) outerResultset.getObject(column number/label)) {
    while(innerResultset.next()) {
    ...
}

One comment: In many cases, for example when creating "master-detail" queries, you use a correlated Cursor Expression, meaning there is a join on a table that appears in the outer query.