A unique constraint fails on the first duplicate it meets and tells you about only one. Here is how to list them all and clean up safely.
Value Histograms: Counting Rows per Range Bucket in T-SQL
Turn a column of amounts into a clear shape. Three small traps decide whether your bucket counts are true: empty buckets, uneven ranges and BETWEEN.
PIVOT and UNPIVOT: Aggregation, NULLs and Cross-Tab Queries
PIVOT and UNPIVOT reshape SQL Server data. See a tested example, disappearing NULLs, aggregation and fixed cross-tab columns.
STRING_AGG Order: Keep NULLs and Type Width Visible
STRING_AGG order belongs inside WITHIN GROUP. This example preserves duplicate labels, shows how NULL differs from empty text and casts to nvarchar(max) before aggregation.
GROUP BY Done Right
GROUP BY Done Right separates row filters from group filters, handles NULL groups, and avoids totals inflated by careless joins.