INSERT, UPDATE, DELETE and MERGE: OUTPUT, Upserts and Working Safely Against an UPDATE Without WHERE
T-SQL's UPDATE ... FROM raises no error when several source rows match one target row, and which value it writes is undefined; MERGE stops with error 8672. We cover multi-row INSERT, new ids with OUTPUT, the standard correlated UPDATE, the log difference between DELETE and TRUNCATE, MERGE traps, an explicit upsert and safe working with a @@ROWCOUNT check, with real output.
8 Nov 2026
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14 min
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6
