Find Duplicate Records Like a Pro (Zero to Pro)

Duplicate rows sneak into every real database — a retried insert, a bad import, a missing constraint. This video takes you from "what even counts as a duplicate" to a precise, production-safe cleanup query. We cover what counts as a duplicate exact byte-for-byte copies vs. business-key duplicates where a timestamp or other column differs, detecting duplicates with GROUP BY + HAVING COUNT(*) greater 1, why GROUP BY can tell you what's duplicated but not which individual row to delete, ranking rows with the ROW_NUMBER window function using PARTITION BY and ORDER BY, wrapping that in a CTE and deleting WHERE row_number greater 1 in one safe query, the older self-join alternative for engines without window functions, and why indexing the columns you group or partition on matters for performance on large tables. TIMESTAMPS 0:00 Intro — Find Duplicate Records Like a Pro 0:14 Define The Enemy — What Counts As A Duplicate? 0:39 Step 1: GROUP BY + HAVING — Detect Duplicates 1:04 The Catch — GROUP BY Can't Tell You Which Row 1:29 Step 2: ROW_NUMBER() — Rank Every Row 1:56 Step 3: CTE + DELETE — Remove The Redundant Rows 2:21 The Older Way — The Self-Join Alternative 2:52 Performance Note — Index What You Group Or Partition By 3:13 Recap — The Real Workflow If this finally made SQL deduplication click, consider subscribing for more deep dives like this.