Answer
SQL Server uses hash match for large, unsorted datasets where hashing is cheaper than repeated seeks.
Poor row estimates may also cause SQL to choose hashing, sometimes leading to spills.
Quick Answer
SQL Server chooses Hash Match when it can't sort both inputs efficiently (no useful index, large unsorted data). It builds a hash table from the smaller input and probes it with the larger. It's memory-intensive and can spill to TempDB if the memory grant was underestimated. More common with missing or outdated indexes.
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SugharaIQ Editorial Team
Verified Answer
This answer has been peer-reviewed by industry experts holding senior engineering roles to ensure technical accuracy and relevance for modern interview standards.
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Source: SugharaIQ