Please explain following code:

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I am not able to get the meaning of choose function and grouping_id in the query.
This is Adventures database in sql server.

Specifically,

CHOOSE (1+ GROUPING_ID(a.CountryRegion) + GROUPING_ID(a.StateProvince) + GROUPING_ID(a.City),
        a.City + ' Subtotal', a.StateProvince + ' Subtotal',
        a.CountryRegion + ' Subtotal', 'Total'

My question is regarding the choose clause. As per the syntax , it is

CHOOSE ( index, val_1 val_2 [, val_n ] )

Furthermore, "grouping_id" should contain all list of columns which are in "GROUP BY".

If you could refer even to some article on grouping id.

I did my google search. What I understood seems insufficient.

Thanks for help

What I have tried:

C#

SELECT a.CountryRegion, a.StateProvince, a.City,
CHOOSE (1+ GROUPING_ID(a.CountryRegion) + GROUPING_ID(a.StateProvince) + GROUPING_ID(a.City),
        a.City + ' Subtotal', a.StateProvince + ' Subtotal',
        a.CountryRegion + ' Subtotal', 'Total') AS Level,
SUM(soh.TotalDue) AS Revenue
FROM SalesLT.Address AS a
JOIN SalesLT.CustomerAddress AS ca
ON a.AddressID = ca.AddressID
JOIN SalesLT.Customer AS c
ON ca.CustomerID = c.CustomerID
JOIN SalesLT.SalesOrderHeader as soh
ON c.CustomerID = soh.CustomerID
GROUP BY ROLLUP(a.CountryRegion, a.StateProvince, a.City)
ORDER BY a.CountryRegion, a.StateProvince, a.City;

Posted 5-Jun-18 5:39am

Member 13842073

Updated 6-Jun-18 5:19am

v3

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Comments

CHill60 5-Jun-18 11:57am

Have you read the documentation?
CHOOSE (Transact-SQL) | Microsoft Docs[^]
GROUPING_ID (Transact-SQL) | Microsoft Docs[^]

Member 13842073 5-Jun-18 13:03pm

Yes, I did read that. Still not clear

2 solutions

Solution 1

No.
Do you have any idea how much work explaining code line by line is?
Every single line needs a paragraph of explanation! For example:

int next = r.Next();

Create a new variable called "next" which can hold a integer value. From the previously declared Random instance "r", call the "Next" method to get a new random number, and assign it to the "next" variable.

Can you imagine how long it would take us to explain even a very short code fragment like your example, line by line?

No. It is not going to happen. If you have a specific problem, then ask a question about it. But think first - would you want to sit down for 45 minutes and type up a line-by-line description for no good reason?

Posted 5-Jun-18 6:19am

OriginalGriff

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Richard Deeming · Accepted Answer · 2018-06-06T05:21:00

Quote:
"grouping_id" should contain all list of columns which are in "GROUP BY"

Read the documentation again:

GROUPING_ID (Transact-SQL) | Microsoft Docs[^]:
Each GROUPING_ID argument must be an element of the GROUP BY list.

You are grouping by a.CountryRegion, a.StateProvince, and a.City, so each of those column names is a valid argument for the GROUPING_ID aggregate function.

Quote:
My question is regarding the choose clause. As per the syntax , it is
CHOOSE ( index, val_1 val_2 [, val_n ] )

And that's exactly what you have:

CHOOSE (
    /* index = */  1 + GROUPING_ID(a.CountryRegion) + GROUPING_ID(a.StateProvince) + GROUPING_ID(a.City),
    /* val_1 = */  a.City + ' Subtotal',
    /* val_2 = */  a.StateProvince + ' Subtotal',
    /* val_3 = */  a.CountryRegion + ' Subtotal', 
    /* val_4 = */  'Total'
)

To understand the query properly, you'll also need to understand the ROLLUP clause:
SQL SERVER - Introduction to Rollup Clause - SQL Authority with Pinal Dave[^]