Question

I have an SQLite database that stores a list of items with categories. Categories are implicit, there is no separate table for them. I would like a single query that would return all items ordered by category, with an extra row per category.

Consider the following scenario:

ID    Name       Category
1     Item 1     C1
2     Item 2     C2
3     Item 3     C1

The results I expect would be something like:

ID    Name       Category
null  null       C1
1     Item 1     C1
3     Item 3     C1
null  null       C2
2     Item 2     C2

This is to have a direct mapping to the list view where the results will be displayed, that contain an extra separator item per category. What I’m doing right now is return all elements ordered by category, and iterate over all of them to know where the separators should be located.

I have experimented with a number of different JOINs, but my SQL-fu is weak and I cannot figure out how to write such query. How would I go about doing this? Which SQL constructs would let me add those extra rows? Is it even possible to get the results in the way I need them in a single -no matter how complex- query?

Answer 1

Consider a union:

select  ID    
,       Name
,       Category
union all
select  distinct null
,       null
,       Category
order by 
        Category

An order by applies to the entire union– no need for a subquery.