How can I count replicate values across columns? - sql

Question

I have a fairly simple problem that I need to solve by SQL>
There is a database that has several columns of values that are duplicate. I am trying to count the number of values that occurs across those columns. I need to know how many values for each category. For example, if there is a column for different types of cookies that one bakery sells; chocolate and raisin and another column has types of cookies that other bakery sells including chocolate and raisin, I want to know how many chocolate cookies all the bakeries sell.
My query:
SELECT types_cookies_store01. COUNT(*) FROM cookies
GROUP BY types_cookies_store01
This code is returning only one column's count but how can I know the count across all the columns?
Thank you!

Answer 1

Your data model is poor!
Assuming it is equal to this:
| types_cookies_store01 | types_cookies_store02 | types_cookies_store03 |
|-----------------------|-----------------------|-----------------------|
| A | | |
| C | | |
| | A | |
| A | | |
| B | | |
| | B | |
| | | B |
| C | | |
| | C | |
Don't use a new column for each store, use one column to specify the store:
| Cookietype | Store |
|------------|-------|
| A | 01 |
| A | 03 |
| B | 02 |
| B | 01 |
| A | 02 |
| C | 02 |
| D | 02 |
| B | 03 |
| B | 01 |
| A | 03 |
| C | 03 |
Now you can group by Cookietype to get sales of all stores.
Select Cookietype, Count(Cookietype) as CountOfCookieType
From SalesTable
Group By Cookietype
Or to get sales by store add the Store to the group by:
Select Cookietype, Store, Count(Cookietype) as CountOfCookieType
From SalesTable
Group By Cookietype, Store
With that data model you can add (almost) unlimited new stores.
With your data model you need a new column for each new store and tables are limited to 255 columns!
You can work around your poor model, by using a union query:
SELECT UnionCols.Cookietype, COUNT(*)
FROM (
SELECT types_cookies_store01 As Cookietype, 'Store01' As Store
FROM cookies
WHERE Not types_cookies_store01 Is Null
UNION ALL
SELECT types_cookies_store02 As Cookietype, 'Store02' As Store
FROM cookies
WHERE Not types_cookies_store02 Is Null
UNION ALL
SELECT types_cookies_store03 As Cookietype, 'Store03' As Store
FROM cookies
WHERE Not types_cookies_store03 Is Null
) As UnionCols
Group By UnionCols.Cookietype
But performance will be poor on large data and new stores are hard to add.
It is strongly recommended to improve your data model instead of working around it!
Some links to read:
Database design basics
Access All In One