How do I create a loop, or a way to use the results of previous SELECT statements into the next SELECT statement?

Question

I have a database with a nested hierarchy structure. At the high levels of the hierarchy, there aren't any actual typeIDs (individual items) associated with a given marketGroupID .

Instead, I start at the top using a string search to find the categories I want. I need to keep going down in the hierarchy by using the marketGroupIDs I've selected as the parentGroupIDs for the next search so that I find all IDs within that subcategory. This keeps dividing into more subcategories until the column hasTypes = 1 (there are typeIDs associated with this subcategory).

While I'm currently pursuing a very manual option: keep making another search until I get to the level I want, is there a way to construct a loop that keeps SELECTING based upon WHERE marketGroupID X = parentGroupID Y, and hasTypes = 0 ?

MANUAL METHOD I'M TRYING TO REPLACE

The columns I am mainly working with are marketGroupID and parentID. What I've tried so far is using c.fetchall() to get the previous result and put it in a variable next_input. Then I use the parameter '?' using sqlite3 in Python. The issue with this is that the number of inputs can change, as the previous SELECT statement will give me a list of tuples that could be anywhere from sixty to several hundred long.

c.execute("""SELECT marketGroupID FROM invMarketGroups WHERE parentGroupID IN (SELECT marketGroupID FROM invMarketGroups WHERE marketGroupName='Ships' 
OR marketGroupName = 'Ship Equipment' OR marketGroupName = 'Implants & Boosters')""");

Next search step.

python next_input = c.fetchall()

So, taking the time to make the number of these equal to list length, I've managed to make it work by turning the result into a single list:

next_input = [i[0] for i in next_input]

c.execute("SELECT marketGroupID FROM invMarketGroups WHERE parentGroupID IN ({idlist_formatted})".format(idlist_formatted= ','.join(['?']*len(next_input))), next_input)

How do I make a loop so that it keeps running recursively that ends until hasTypes != 0, grabbing marketGroupIDs where hasTypes = 1?

Answer 1

Sqllite supports recursive queries which can be used for hierarchical queries (which is what you are trying to do). Take a look at the documentation here It even has a section about hierarchical queries. This way you can completely replace your loop with one call to the DB and let it do the work.