How to get substring for filter and group by clause in AWS Redshift database

Question

How to get substring from column which contains records for filter and group by clause in AWS Redshift database.

I have table with records like:

Table_Id         


        

Answer 1

If you have at most 3 values in any "categories" cell you can unnest the cells, get the list of unique values and use that list in a join condition like this:

WITH
values as (
    select distinct category
    from (
            select distinct split_part(categories,';',1) as category from your_table
            union select distinct split_part(categories,';',2) from your_table
            union select distinct split_part(categories,';',3) from your_table
     )
     where nullif(category,'') is not null
)
SELECT
 t2.category
,sum(t1.value)
FROM your_table t1
JOIN values t2
ON split_part(categories,';',1)=t2.category
OR split_part(categories,';',2)=t2.category
OR split_part(categories,';',3)=t2.category

if you have more than 3 options just add another split_part level both in WITH part and the join condition