DISTINCT vs GROUP BY for Whole Rows

Concepts covered: sqlWindowDedup

The simplest case: the rows are byte-for-byte identical, and you want one copy of each. SELECT DISTINCT is the one-line answer. It is the right tool when every column has the same value across duplicate rows, which happens with CSV imports where someone duplicated a region, with UNION ALL queries that should have been UNION, and with simple lookup tables. Anything more complex needs the next section's tool. The DISTINCT pattern DISTINCT considers all columns in the SELECT list together. Two rows are duplicates only if every column matches. The result has one row per unique combination of (customer_id, email, signup_date, segment). The row count drops if there were duplicates; the row count stays the same if every row was already unique. DISTINCT vs UNION vs GROUP BY (the three forms that d

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