What is Spool Operator in SQL Server: SQL Server Performance Tuning
Spool operator scans the input and places a copy of each row in a hidden spool table that is stored in the tempdb database and existing o...

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Spool operator scans the input and places a copy of each row in a hidden spool table that is stored in the tempdb database and existing only for the lifetime of the query. If the operator is rewound (for example, by a Nested Loops operator) but no rebinding is needed, the spooled data is used instead of re-scanning the input.
Table Spool is a physical operator.
Table Spool is a physical operator.