512: Subquery returned more than 1 value
SQL ServerWhat does it mean?
A subquery used in a context expecting a single value (=, <, >, comparison or assignment) returned more than one row. SQL Server expected a single scalar value but encountered multiple values.
Why does it happen?
A subquery assumed to return a single value for the comparison returns multiple rows, a non-unique match condition, a missing filter, or an incorrectly constructed correlated query.
How to fix it
Reduce the subquery to a single row (e.g. TOP 1, MAX/MIN, or an appropriate GROUP BY). If multiple values are expected, use IN or EXISTS instead of =. Rewrite with a JOIN. Investigate why the subquery returns multiple rows and fix the filter/key conditions.
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