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  1. MariaDB Server
  2. MDEV-29228

Odd EXPLAIN FORMAT=JSON output for SELECT DISTINCT ... GROUP BY query

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      Description

      create table t2 (a int, b int);
      insert into t2 select seq/100, seq from seq_1_to_1000;
      explain format=json select distinct 1+max(b) from t2 group by a;
      

      gives

        "query_block": {
          "select_id": 1,
          "filesort": {
            "sort_key": "t2.a",
            "duplicate_removal": {
              "temporary_table": {
                "temporary_table": {
                  "nested_loop": [
                    {
                      "table": {
                        "table_name": "t2",
                        "access_type": "ALL",
                        "rows": 1000,
                        "filtered": 100
                      }
                    }
                  ]
                }
              }
            }
          }
        }
      }
      

      note the

              "temporary_table": {
                "temporary_table": {
      

      part.

      This doesn't allow one to understand the purpose of the temporary tables.

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              Assignee:
              psergei Sergei Petrunia
              Reporter:
              psergei Sergei Petrunia
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                Updated:

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