SQL Lookup data in joined table based on LIKE value stored in joined table column

Question

I am trying to build a query that will look up a product_subcategory based on a reference data in a user entered table and joining two tables together. My database is SQL Server 2012 Express.

First the products table has three columns: Product_id (unique identifier), event_id (INT data type), and product_category. (product_category needs to be alphanumeric currently varchar(32) data type)

Example Products table data:

Product_id  event_id    product_category
1           20          100
2           20          105
3           20          200
4           21          100
5           21          200
6           21          203
7           22          105
8           22          207

Second the events table has two columns: event_id (unique identifier, INT Data type) and zone (float data type, not sure why this was setup as float, probably should have been INT but its a pre-existing table and I don't want to change it)

event_id      zone
20            1
21            2
22            3

Third the subcategory table has four columns: subcategory_id (unique identifier, INT data type), zone (joins to zone column in products table, INT Data type), category_lookup (varchar(max) data type), and product_subcategory (varchar(50) data type). This is a table that I am creating for this project so I can change the structure or datatypes to be whatever is needed for the project, I don't have that flexibility on the other tables.

Example Subcategory table data:

subcategory_id  zone    category_lookup    product_subcategory
1               1       '1%'               25
2               1       '2%'               23
3               2       '1%'               26
4               2       '2%'               30

I want to build a query that will search the product table and match a zone, product_category, and product_subcategory together based on the value in the subcategory.category_lookup column.

The data that I want returned from the query is:

product_ID  zone    product_category    product_subcategory
1           1       100                 25
2           1       105                 25
3           1       200                 23
4           2       100                 26
5           2       200                 30
6           2       203                 30
7           3       105                 NULL or 'N/A'
8           3       107                 NULL or 'N/A'

The logic behind looking up the matching subcategory will be similar to below: (this is essentially what is stored in the subcategory table) (the text in the “quotes” is what I mean by reference data, and will be user entered)

IE... if zone = 1 and product_category “begins with 1” then product_subcategory = 25
IE... if zone = 1 and product_category “begins with 2” then product_subcategory = 23
IE... if zone = 2 and product_category “begins with 1” then product_subcategory = 26
IE... if zone = 2 and product_category “begins with 2” then product_subcategory = 30

I do understand that one of the issues with my logic is that if multiple subcategories match to one product then it will throw an error, but I think I can code around that once I get this part of it working

I am fine going a different direction with this project but this is the first way I decided to tackle it. The most important component is that the product_subcategory’s are going to be located in a separate user entered table, and there needs to be user entered logic as discussed above to determine the product_subcategory based on zone and product_category.

I am not a SQL guru at all so I don’t even know where to start to handle this problem. Any advice is appreciated.

Based on answers I have received so far I have come up with this:

SELECT p.product_id, p.event_id, e.zone, p.product_category, sc.product_subcategory
FROM Products p
LEFT JOIN events e on p.event_id = e.event_id
LEFT JOIN SubCategory sc ON e.zone = sc.zone AND CAST(p.product_category as varchar(max)) like sc.category_lookup

But unfortunately its only returning NULL for all of the product_subcategory results.

Any additional help is appreciated. Thanks,

Answer 1

This should do the trick, you will just need to modify the CAST(p.zone as nchar(10)) to insert the correct data type for your category_lookup column, in place of nchar(10), as I assume the zone in Products is an int where as the lookup column is some string based column:

SELECT p.product_id, p.zone, p.product_category, sc.product_subcategory
FROM Products p
LEFT JOIN SubCategory sc ON p.zone = sc.zone
AND CAST(p.zone as nchar(10)) like sc.category_lookup

Based on your updates, the following should work:

SELECT p.product_id, p.event_id, e.zone, p.product_category, 
       sc.product_subcategory
FROM Products p
INNER JOIN events e on p.event_id = e.event_id
LEFT OUTER JOIN SubCategory sc ON e.zone = sc.zone 
     AND CAST(e.zone as nchar(250)) LIKE CAST(sc.category_lookup as nchar(250))

Update based on comments:

SELECT p.product_id, p.event_id, e.zone, p.product_category, 
       sc.product_subcategory
FROM Products p
INNER JOIN events e on p.event_id = e.event_id
LEFT OUTER JOIN SubCategory sc ON e.zone = sc.zone 
     AND CAST(p.product_category as nchar(250)) LIKE sc.category_lookup

Working sample SQLFiddle

Answer 2

Not tested but is this what you're looking for ?

select a.product_ID, a.zone, a.product_category, b.product_subcategory
from Products a
inner join Subcategory on ((a.zone = b.zone) and (a.product_category like b.category_lookup))

Answer 3

Try this..

select p.product_id, p.zone, p.product_category, isnull(s.product_subcategory,'NA') as product_subcategory
from Products p
left outer join Subcategory s on (s.zone = p.zone and p.product_category like s.category_lookup);