SQL filter for parent child tree structure

Question

So I have a database where each record has a reference to a parent record in the same table (possibly null). Each record also has an 'active' flag that describes whether the single record is currently active.

I would like to end up with a flat list of records that have the following traits:

• Is active
• Contains no inactive ancestors

Instead of constructing the tree and doing a search to filter out the records I would like to accomplish this in SQL. Is there a way to join or aggregate to filter out the undesired records?

Answer 1

You can achieve this using CTEs and recursive querying (if your database system supports it).

There is a SQL Server example here and a Postgres example here.