How do you identify blocking or long-running queries (interview theory + DMV)?

Short answer: Talk about DMVs: sys.dm_exec_requests, sys.dm_exec_sessions, sys.dm_os_waiting_tasks, and reading plans. For query writing interviews, also discuss indexes, sargability, and avoiding SELECT *.

Sample solution

SELECT r.session_id, r.status, r.command, r.wait_type, r.blocking_session_id,
       t.text
FROM sys.dm_exec_requests r
CROSS APPLY sys.dm_exec_sql_text(r.sql_handle) t
WHERE r.session_id <> @@SPID;

Even app developers score points naming DMVs and “parameter sniffing” briefly.