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SQL problems involving graph-like relationships and self-joins are common in technical interviews at large tech companies. While this exact problem may not always appear, similar patterns involving hierarchical or indirect relationships are frequently tested.
The optimal approach uses a SQL self-join on the follow table. By joining the table with itself, you can connect follower chains such as A → B and B → C, revealing second-degree followers. The results are then grouped by the final user and counted.
Key SQL concepts include self-joins, grouping, and aggregate functions like COUNT. Understanding how to relate rows within the same table is crucial since the relationship chain is stored in a single table.
The table represents a directed graph where users are nodes and follow relationships are edges. The problem essentially asks you to find paths of length two in this graph and count the starting nodes for each destination node.