GROUP BY
In an earlier exercise, you wrote a separate WHERE query to determine the amount of demand lost for a specific region. We wouldn't want to have to write individual queries for every region. Fortunately, you don't have to write individual queries for every region. With GROUP BY, you can obtain a sum of all the unique values for your chosen column, all at once.
You'll return to the grid table here and calculate the total lost demand for all regions.
Latihan ini adalah bagian dari kursus
Introduction to SQL Server
Petunjuk latihan
- Select
nerc_regionand the sum ofdemand_loss_mwfor each region. - Exclude values where
demand_loss_mwis NULL. - Group the results by
nerc_region. - Arrange in descending order of
demand_loss.
Latihan interaktif praktis
Cobalah latihan ini dengan menyelesaikan kode contoh berikut.
-- Select the region column
SELECT
___,
-- Sum the demand_loss_mw column
SUM(___) AS demand_loss
FROM
grid
-- Exclude NULL values of demand_loss
WHERE
demand_loss_mw ___ ___ ___
-- Group the results by nerc_region
___ __
nerc_region
-- Order the results in descending order of demand_loss
ORDER BY
demand_loss ___;