Some of the OLAP Function Introduced in the Oracle9i Onwards are Very handy when it comes to do aggregations at
Different Levels .
      For example Rollup Function can be Used forGetting theSubtotals and Grand totals in Just a Single Query Instead of
      Using Many Sub queries.
      Using the Rollup FunctionFor Getting the Subtotals andGrand totals .
      This place I am Just givinga Demo of Using the Rollup and the Grouping Functions.

      SELECTT.STRSTMPAPTYPE , COUNT(T.STRSTMSTDID)FROM TBLSTMTOT T
      GROUP BY ROLLUP(T.STRSTMPAPTYPE)

      CREATE PUBLIC SYNONYM REG FOR TBLSATSRGSTDREG
 

      SELECT T.INTSTGGROUPID , T.STRSTGCLASS ,COUNT(T.STRSRGSTDID)
      FROM REG T
      GROUP BY ROLLUP(T.INTSTGGROUPID , T.STRSTGCLASS)
 

      SELECT T.INTSTGGROUPID , T.STRSTGCLASS ,COUNT(T.STRSRGSTDID),
      GROUPING(T.INTSTGGROUPID) AS "1",
      GROUPING(T.STRSTGCLASS) AS "2"
      FROM REG T
      GROUP BY ROLLUP(T.INTSTGGROUPID , T.STRSTGCLASS)
 

      SELECT T.INTSTGGROUPID
      ,dECODE(GROUPING(T.INTSTGGROUPID)+GROUPING(T.STRSTGCLASS),1,'SUBTOTAL' ,
      2, 'GRAND TOTAL',T.STRSTGCLASS) ,
      COUNT(T.STRSRGSTDID), GROUPING(T.INTSTGGROUPID) AS "1",
      GROUPING(T.STRSTGCLASS) AS "2"
      FROM REG T
      GROUP BY ROLLUP(T.INTSTGGROUPID , T.STRSTGCLASS)
 

      SELECT T.INTSTGGROUPID ,
      DECODE(GROUPING(T.INTSTGGROUPID)+GROUPING(T.STRSTGCLASS),1,'TOTAL OF SCHOOL' ,
      2, 'GRAND TOTAL',T.STRSTGCLASS) AS "CLASS" ,
      COUNT(T.STRSRGSTDID) "STUDENT COUNT"
      FROM REG T
      WHERE T.INTSTGGROUPIDIN (67,99)
      GROUP BY ROLLUP(T.INTSTGGROUPID , T.STRSTGCLASS)
 

      SELECT T.INTSTGGROUPID ,
      DECODE(GROUPING(T.INTSTGGROUPID)+GROUPING(T.STRSTGCLASS),1,'TOTAL OF SCHOOL' ,
      2, 'GRAND TOTAL',T.STRSTGCLASS) AS "CLASS" ,
      COUNT(T.STRSRGSTDID) "STUDENT COUNT"
      FROM REG T
      GROUP BY ROLLUP(T.INTSTGGROUPID , T.STRSTGCLASS)
      having GROUPING(T.INTSTGGROUPID)+GROUPING(T.STRSTGCLASS) >0
 

As a note, it is possible to calculate the same results using only SQL Select, without the ROLLUP clause and without
programming.
This uses several SELECTs joined by UNION ALL.These tend to be complicated to write and less efficient to execute.

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