17.10 - PARTITION BY Phrase - Advanced SQL Engine - Teradata Database

PARTITION BY takes a column reference list and groups the rows based on the specified column reference list over which the ordered analytical function executes. Such a grouping is static. To define a group or partition based on a condition, use the RESET WHEN phrase. For more information, see RESET WHEN Phrase.

If there is no PARTITION BY phrase or RESET WHEN phrase, then the entire result set, delivered by the FROM clause, constitutes a single partition, over which the ordered analytical function executes.

Consider the following table named sales_tbl.

The following SELECT statement, which does not include PARTITION BY, computes the average sales for all the stores in the table:

   SELECT StoreID, SMonth, ProdID, Sales, 
   AVG(Sales) OVER () 
   FROM sales_tbl;
   
   StoreID  SMonth  ProdID      Sales  Group Avg(Sales)
   -------  ------  ------  ---------  ----------------
      1001       1  C        35000.00          47083.33
      1001       2  C        25000.00          47083.33
      1001       3  C        40000.00          47083.33
      1001       4  C        25000.00          47083.33
      1001       5  C        30000.00          47083.33
      1001       6  C        30000.00          47083.33
      1002       1  C        40000.00          47083.33
      1002       2  C        35000.00          47083.33
      1002       3  C       110000.00          47083.33
      1002       4  C        60000.00          47083.33
      1002       5  C        35000.00          47083.33
      1002       6  C       100000.00          47083.33
   

To compute the average sales for each store, partition the data in sales_tbl by StoreID:

   SELECT StoreID, SMonth, ProdID, Sales, 
   AVG(Sales) OVER (PARTITION BY StoreID)
   FROM sales_tbl;
   
   StoreID  SMonth  ProdID      Sales  Group Avg(Sales)
   -------  ------  ------  ---------  ----------------
      1001       3  C        40000.00          30833.33
      1001       5  C        30000.00          30833.33
      1001       6  C        30000.00          30833.33
      1001       4  C        25000.00          30833.33
      1001       2  C        25000.00          30833.33
      1001       1  C        35000.00          30833.33
      1002       3  C       110000.00          63333.33
      1002       5  C        35000.00          63333.33
      1002       6  C       100000.00          63333.33
      1002       4  C        60000.00          63333.33
      1002       2  C        35000.00          63333.33
      1002       1  C        40000.00          63333.33