Bug 211839 String grouping unit type needs to support interval range.
Build ID: I20071101-2000 As Chart has supported, the String grouping unit type can be set interval range, the interval range means that the string group will base on row count distinction. For instance, let's say we have a,b,c,d,e,f,g , and set interval range to 2, the grouping result should be a,c,e,g. Now it is a requirement that DtE support the grouping type.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/odi/IQuery.java
public static final int NO_SORT = -1;		 
    	public static final int SORT_ASC = 0;		
    	public static final int SORT_DESC = 1;		
        
        private String keyColumn;
        private int keyIndex;
        private String name;
    	private int sortDirection = NO_SORT;        
        private int interval = NO_INTERVAL;
        private boolean isComplexExpression = false;
        private double intervalRange = 0;
        private Object intervalStart;
        private int dataType;
        private List filters;
        private List sorts;
    	/**
    	 * Instantiates a groupSpec defining a column name
    	 * as its required group key.
    	 * @param groupKeyColumn The column name as the group key.
    	 */
        public GroupSpec( String groupKeyColumn )
		{
			keyIndex = -1;
			keyColumn = groupKeyColumn;
		}
        
    	/**
    	 * Instantiates a groupSpec defining a column name
    	 * as its required group key.