How do I group by on calculated columns?

Question

Assume the following table with 3 numeric fields:

Images (table)
--------------
Width
Height
Amount

Width and Height are image sizes in millimeters. Now I want to create a report about the amount of images grouped by their dimensions in centimeters. This means that I have to GROUP BY 2 non existing columns.

I can do:

SELECT      ROUND(Width/10,0)   AS W
        ,   ROUND(Height/10,0)  AS H
        ,   SUM(Amount)         AS A 
FROM        IMAGES
GROUP BY    Width
        ,   Height 
ORDER BY    W
        ,   H
        ,   A

but this will do the mm to cm conversion only on the view level and will result in more than one row for same dimensions.

eg

 W   H  A
--- --- - 
150 159 2
150 160 1

will not result in 1 category

W  H  A
-- -- - 
15 16 3

but in

W  H  A
-- -- - 
15 16 2
15 16 1

The targeted engine is actually a FileMaker database, that unfortunatly does not seem to support aggregate functions within the GROUP BY clause.

Answer 1

Simply GROUP BY your calculated columns:

SELECT 
    ROUND(Width/10,0) as W
    ,ROUND(Height/10,0) as H
    ,COUNT(*) as A -- You may replace this with SUM(Amount) too
FROM 
    IMAGES
GROUP BY 
    ROUND(Width/10,0)
    ,ROUND(Height/10,0)
ORDER BY 
    W
    ,H
    ,A

EDIT: Also, from what I understand of your question you want the COUNT not the SUM of the rows..., right?

Answer 2

Following query uses Common Table Expression (CTE) to convert width and height from mm to cm along with rounding and then produces a derived table output. This CTE output is then used to group the width and height values to calculate the SUM of the amount column.

I am not sure if you were looking for SUM of the amount column or the COUNT of the amount column. I assumed SUM based on your query. If you only want COUNT , please change SUM in the query to COUNT .

Click here to view the demo in SQL Fiddle

Script :

CREATE TABLE images
(
        width   INT     NOT NULL
    ,   height  INT     NOT NULL
    ,   amount  FLOAT   NOT NULL
);

INSERT INTO images (width, height, amount) VALUES
    (150, 159, 1),
    (150, 159, 2),
    (150, 158, 1),
    (150, 159, 3),
    (150, 158, 2),
    (160, 158, 4),
    (160, 158, 1);

;WITH imagesincm AS
(
    SELECT      ROUND(width  / 10,0)    AS W
            ,   ROUND(height / 10,0)    AS H
            ,   amount
    FROM        images
) 
SELECT      W
        ,   H
        ,   COUNT(amount) AS A
FROM        imagesincm
GROUP BY    W
        ,   H 
ORDER BY    W
        ,   H

Output :

W  H  A
-- -- - 
15 15 9
16 15 5

Answer 3

根据官方 FileMaker SQL 参考 ( https://help.claris.com/en/sql-reference.pdf ) 的第 11 页，Group By 子句仅适用于字段。