Bug 139110 GUI enhancement to support create subquery more conveniently.
Description: GUI enhancement to support create subquery more conveniently. Steps to reproduce: Subquery means insert table/list inside another table/list item, and the inner table/list item doesn't has its own dataset binding. In latest build, if you want to creat a subquery structure, you have to use dataSetRow as binding expression for data items in inner table/list item. For example: 1. Insert a list, generate column data binding for it. 2. Add a group for the list. 3. Insert table to list group header which is used to display data rows in list group. Dont' bind table to dataset. 4. Insert a data to table detail row. 5. New a binding column for data, click to Open Expression Builder. The issue is that only "Availabel column bindings" is listed in Category but no "Available Data Sets". So I have to type dataSetRow[".."] by myself to generate correct subquery. For users, maybe they will mistakenly use "Available column bindings" which will generate expression like row._outer[".."] and get wrong result. So it is recommended to add "Available Data Sets" in Expression Builder for such case.
UI/org.eclipse.birt.report.designer.core/src/org/eclipse/birt/report/designer/util/DEUtil.java
result = (ReportItemHandle) handle;
			}
			return result;
		}
		return null;
	}
	/**
	 * Add a binding column on the given element
	 * 
	 * @param handle
	 *            the handle of the elementIt should be a ReportItemHandle or a
	 *            GroupHandle
	 * @param column
	 *            the column to add
	 * @param inForce
	 *            true to add the column with duplicated expression,or false not
	 *            to do
	 * 
	 * @return the handle of the binding column,or null if failed
	 */
	public static ComputedColumnHandle addColumn( DesignElementHandle handle,
			ComputedColumn column, boolean inForce ) throws SemanticException
	{
		Assert.isLegal( handle instanceof ReportItemHandle
				|| handle instanceof GroupHandle );
		if ( handle instanceof GroupHandle )
		{
			return ( (GroupHandle) handle ).addColumnBinding( column, inForce );
		}
		return ( (ReportItemHandle) handle ).addColumnBinding( column, inForce );