In Oracle, it's possible to return a cursor inside a SQL query, using the cursor keyword, like this:
select owner, table_name, cursor (select column_name from all_tab_columns where owner = allt.owner and table_name = allt.table_name) as columns from all_tables allt The questions are:
It's called a CURSOR EXPRESSION, and it is documented in the obvious place, the Oracle SQL Reference. Find it here.
As for your second question, the closest thing PostgreSQL offers to match this functionality is "scalar sub-queries". However, as @tbrugz points out, these only return one row and one column, so they aren't much like Cursor Expressions. Read about them in the documentation here. MySQL also has Scalar Sub-queries, again limited to one column and one row. Docs here. Likewise SQL Server and DB2 (not open source but for completeness).
That rules out all the obvious contenders. So, it seems unlikely any other DBMS offers the jagged result set we get from Oracle's cursor expression.
Postgres provides cursor expressions but the syntax is a bit less handy than Oracle's.
First you need to create function for array to refcursor conversion:
create or replace function arr2crs(arr anyarray) returns refcursor as $$ declare crs refcursor; begin open crs for select * from unnest(arr); return crs; end; $$ language plpgsql volatile; Now let's create some test data
create table dep as select 1 depid, 'Sales' depname union all select 2 depid, 'IT' depname; create table emp as select 1 empid, 1 depid, 'John' empname union all select 2 empid, 1 depid, 'James' empname union all select 3 empid, 2 depid, 'Rob'; You can query it like this
select dep.*, arr2crs(array( select row(emp.*)::emp from emp where emp.depid = dep.depid )) emps from dep And process in on client side like this (Java)
public static List Rs2List(ResultSet rs) throws SQLException{ List result = new ArrayList(); ResultSetMetaData meta = rs.getMetaData(); while(rs.next()){ Map row = new HashMap(); for (int i = 1; i <= meta.getColumnCount(); i++){ Object o = rs.getObject(i); row.put( meta.getColumnName(i), (o instanceof ResultSet)?Rs2List((ResultSet)o):o); } result.add(row); } return result; } Note that you must explicitly cast row to particular type. You can use CREATE TYPE to create necessary types.