EXPLAIN - Hash Join


Build a hash table from the inner table, keyed by the join key. Then scan the outer table, checking if a corresponding value is present. If the hash table would exceed work_mem, this process needs to happen in several batches writing temporary files to disk, which becomes dramatically slower.

Important Fields:

  • Filter
  • Hash Cond
  • Inner Unique
  • Join Filter
  • Join Type
  • Rows Removed by Filter
  • Rows Removed by Join Filter

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