{
  "steps": [
    {
      "join_preparation": {
        "select#": 1,
        "steps": [
          {
            "join_preparation": {
              "select#": 2,
              "steps": [
                {
                  "expanded_query": "/* select#2 */ select `sk`.`category` from (`sample` `s` join `sample_kind` `sk` on((`sk`.`id` = `s`.`sample_kind_id`))) where (`s`.`id` = `sa`.`sample_id`)"
                }
              ]
            }
          },
          {
            "expanded_query": "/* select#1 */ select distinct `sa`.`attribute` AS `attribute` from `sample_attribute` `sa` where ((/* select#2 */ select `sk`.`category` from (`sample` `s` join `sample_kind` `sk` on((`sk`.`id` = `s`.`sample_kind_id`))) where (`s`.`id` = `sa`.`sample_id`)) = 'physiological') order by `sa`.`attribute`"
          }
        ]
      }
    },
    {
      "join_optimization": {
        "select#": 1,
        "steps": [
          {
            "condition_processing": {
              "condition": "WHERE",
              "original_condition": "((/* select#2 */ select `sk`.`category` from (`sample` `s` join `sample_kind` `sk` on((`sk`.`id` = `s`.`sample_kind_id`))) where (`s`.`id` = `sa`.`sample_id`)) = 'physiological')",
              "steps": [
                {
                  "transformation": "equality_propagation",
                  "subselect_evaluation": [
                  ],
                  "resulting_condition": "((/* select#2 */ select `sk`.`category` from (`sample` `s` join `sample_kind` `sk` on((`sk`.`id` = `s`.`sample_kind_id`))) where (`s`.`id` = `sa`.`sample_id`)) = 'physiological')"
                },
                {
                  "transformation": "constant_propagation",
                  "subselect_evaluation": [
                  ],
                  "resulting_condition": "((/* select#2 */ select `sk`.`category` from (`sample` `s` join `sample_kind` `sk` on((`sk`.`id` = `s`.`sample_kind_id`))) where (`s`.`id` = `sa`.`sample_id`)) = 'physiological')"
                },
                {
                  "transformation": "trivial_condition_removal",
                  "subselect_evaluation": [
                  ],
                  "resulting_condition": "((/* select#2 */ select `sk`.`category` from (`sample` `s` join `sample_kind` `sk` on((`sk`.`id` = `s`.`sample_kind_id`))) where (`s`.`id` = `sa`.`sample_id`)) = 'physiological')"
                }
              ]
            }
          },
          {
            "table_dependencies": [
              {
                "table": "`sample_attribute` `sa`",
                "row_may_be_null": false,
                "map_bit": 0,
                "depends_on_map_bits": [
                ]
              }
            ]
          },
          {
            "ref_optimizer_key_uses": [
            ]
          },
          {
            "rows_estimation": [
              {
                "table": "`sample_attribute` `sa`",
                "const_keys_added": {
                  "keys": [
                    "sample_attribute_unique"
                  ],
                  "cause": "distinct"
                },
                "range_analysis": {
                  "table_scan": {
                    "rows": 4050340,
                    "cost": 824901
                  },
                  "potential_range_indices": [
                    {
                      "index": "PRIMARY",
                      "usable": false,
                      "cause": "not_applicable"
                    },
                    {
                      "index": "sample_attribute_unique",
                      "usable": true,
                      "key_parts": [
                        "attribute",
                        "sample_id"
                      ]
                    },
                    {
                      "index": "sample_attribute_FKIndex1",
                      "usable": false,
                      "cause": "not_applicable"
                    }
                  ],
                  "best_covering_index_scan": {
                    "index": "sample_attribute_unique",
                    "cost": 1.18e6,
                    "chosen": false,
                    "cause": "cost"
                  },
                  "setup_range_conditions": [
                  ],
                  "group_index_range": {
                    "distinct_query": true,
                    "potential_group_range_indices": [
                      {
                        "index": "PRIMARY",
                        "usable": false,
                        "cause": "not_covering"
                      },
                      {
                        "index": "sample_attribute_unique",
                        "covering": true,
                        "rows": 107,
                        "cost": 203.3
                      },
                      {
                        "index": "sample_attribute_FKIndex1",
                        "usable": false,
                        "cause": "not_covering"
                      }
                    ]
                  },
                  "best_group_range_summary": {
                    "type": "index_group",
                    "index": "sample_attribute_unique",
                    "group_attribute": null,
                    "min_aggregate": false,
                    "max_aggregate": false,
                    "distinct_aggregate": false,
                    "rows": 107,
                    "cost": 203.3,
                    "key_parts_used_for_access": [
                      "attribute"
                    ],
                    "ranges": [
                    ],
                    "chosen": true
                  },
                  "chosen_range_access_summary": {
                    "range_access_plan": {
                      "type": "index_group",
                      "index": "sample_attribute_unique",
                      "group_attribute": null,
                      "min_aggregate": false,
                      "max_aggregate": false,
                      "distinct_aggregate": false,
                      "rows": 107,
                      "cost": 203.3,
                      "key_parts_used_for_access": [
                        "attribute"
                      ],
                      "ranges": [
                      ]
                    },
                    "rows_for_plan": 107,
                    "cost_for_plan": 203.3,
                    "chosen": true
                  }
                }
              }
            ]
          },
          {
            "considered_execution_plans": [
              {
                "plan_prefix": [
                ],
                "table": "`sample_attribute` `sa`",
                "best_access_path": {
                  "considered_access_paths": [
                    {
                      "access_type": "range",
                      "rows": 107,
                      "cost": 224.7,
                      "chosen": true,
                      "use_tmp_table": true
                    }
                  ]
                },
                "cost_for_plan": 224.7,
                "rows_for_plan": 107,
                "sort_cost": 107,
                "new_cost_for_plan": 331.7,
                "chosen": true
              }
            ]
          },
          {
            "attaching_conditions_to_tables": {
              "original_condition": "((/* select#2 */ select `sk`.`category` from (`sample` `s` join `sample_kind` `sk` on((`sk`.`id` = `s`.`sample_kind_id`))) where (`s`.`id` = `sa`.`sample_id`)) = 'physiological')",
              "attached_conditions_computation": [
              ],
              "attached_conditions_summary": [
                {
                  "table": "`sample_attribute` `sa`",
                  "attached": "((/* select#2 */ select `sk`.`category` from (`sample` `s` join `sample_kind` `sk` on((`sk`.`id` = `s`.`sample_kind_id`))) where (`s`.`id` = `sa`.`sample_id`)) = 'physiological')"
                }
              ]
            }
          },
          {
            "clause_processing": {
              "clause": "ORDER BY",
              "original_clause": "`sa`.`attribute`",
              "items": [
                {
                  "item": "`sa`.`attribute`"
                }
              ],
              "resulting_clause_is_simple": true,
              "resulting_clause": "`sa`.`attribute`"
            }
          },
          {
            "reconsidering_access_paths_for_index_ordering": {
              "clause": "ORDER BY",
              "index_order_summary": {
                "table": "`sample_attribute` `sa`",
                "index_provides_order": true,
                "order_direction": "asc",
                "index": "sample_attribute_unique",
                "plan_changed": false
              }
            }
          },
          {
            "reconsidering_access_paths_for_index_ordering": {
              "clause": "GROUP BY",
              "index_order_summary": {
                "table": "`sample_attribute` `sa`",
                "index_provides_order": true,
                "order_direction": "asc",
                "index": "sample_attribute_unique",
                "plan_changed": false
              }
            }
          },
          {
            "clause_processing": {
              "clause": "GROUP BY",
              "original_clause": "`sa`.`attribute`",
              "items": [
                {
                  "item": "`sa`.`attribute`"
                }
              ],
              "resulting_clause_is_simple": true,
              "resulting_clause": "`sa`.`attribute`"
            }
          },
          {
            "refine_plan": [
              {
                "table": "`sample_attribute` `sa`",
                "access_type": "range"
              }
            ]
          },
          {
            "reconsidering_access_paths_for_index_ordering": {
              "clause": "GROUP BY",
              "index_order_summary": {
                "table": "`sample_attribute` `sa`",
                "index_provides_order": true,
                "order_direction": "asc",
                "index": "sample_attribute_unique",
                "plan_changed": false
              }
            }
          }
        ]
      }
    },
    {
      "join_explain": {
        "select#": 1,
        "steps": [
          {
            "join_optimization": {
              "select#": 2,
              "steps": [
                {
                  "transformations_to_nested_joins": {
                    "transformations": [
                      "JOIN_condition_to_WHERE",
                      "parenthesis_removal"
                    ],
                    "expanded_query": "/* select#2 */ select `sk`.`category` from `sample` `s` join `sample_kind` `sk` where ((`s`.`id` = `sa`.`sample_id`) and (`sk`.`id` = `s`.`sample_kind_id`))"
                  }
                },
                {
                  "condition_processing": {
                    "condition": "WHERE",
                    "original_condition": "((`s`.`id` = `sa`.`sample_id`) and (`sk`.`id` = `s`.`sample_kind_id`))",
                    "steps": [
                      {
                        "transformation": "equality_propagation",
                        "resulting_condition": "((`s`.`id` = `sa`.`sample_id`) and multiple equal(`sk`.`id`, `s`.`sample_kind_id`))"
                      },
                      {
                        "transformation": "constant_propagation",
                        "resulting_condition": "((`s`.`id` = `sa`.`sample_id`) and multiple equal(`sk`.`id`, `s`.`sample_kind_id`))"
                      },
                      {
                        "transformation": "trivial_condition_removal",
                        "resulting_condition": "((`s`.`id` = `sa`.`sample_id`) and multiple equal(`sk`.`id`, `s`.`sample_kind_id`))"
                      }
                    ]
                  }
                },
                {
                  "table_dependencies": [
                    {
                      "table": "`sample` `s`",
                      "row_may_be_null": false,
                      "map_bit": 0,
                      "depends_on_map_bits": [
                      ]
                    },
                    {
                      "table": "`sample_kind` `sk`",
                      "row_may_be_null": false,
                      "map_bit": 1,
                      "depends_on_map_bits": [
                      ]
                    }
                  ]
                },
                {
                  "ref_optimizer_key_uses": [
                    {
                      "table": "`sample` `s`",
                      "field": "id",
                      "equals": "`sa`.`sample_id`",
                      "null_rejecting": false
                    },
                    {
                      "table": "`sample` `s`",
                      "field": "sample_kind_id",
                      "equals": "`sk`.`id`",
                      "null_rejecting": false
                    },
                    {
                      "table": "`sample` `s`",
                      "field": "id",
                      "equals": "`sa`.`sample_id`",
                      "null_rejecting": false
                    },
                    {
                      "table": "`sample_kind` `sk`",
                      "field": "id",
                      "equals": "`s`.`sample_kind_id`",
                      "null_rejecting": false
                    }
                  ]
                },
                {
                  "rows_estimation": [
                    {
                      "table": "`sample` `s`",
                      "table_scan": {
                        "rows": 5244386,
                        "cost": 77120
                      }
                    },
                    {
                      "table": "`sample_kind` `sk`",
                      "table_scan": {
                        "rows": 63,
                        "cost": 1
                      }
                    }
                  ]
                },
                {
                  "considered_execution_plans": [
                    {
                      "plan_prefix": [
                      ],
                      "table": "`sample_kind` `sk`",
                      "best_access_path": {
                        "considered_access_paths": [
                          {
                            "access_type": "ref",
                            "index": "PRIMARY",
                            "usable": false,
                            "chosen": false
                          },
                          {
                            "access_type": "scan",
                            "rows": 63,
                            "cost": 13.6,
                            "chosen": true
                          }
                        ]
                      },
                      "cost_for_plan": 13.6,
                      "rows_for_plan": 63,
                      "rest_of_plan": [
                        {
                          "plan_prefix": [
                            "`sample_kind` `sk`"
                          ],
                          "table": "`sample` `s`",
                          "best_access_path": {
                            "considered_access_paths": [
                              {
                                "access_type": "ref",
                                "index": "PRIMARY",
                                "rows": 1,
                                "cost": 1.2,
                                "chosen": true
                              },
                              {
                                "access_type": "ref",
                                "index": "sample_kind_id",
                                "rows": 1,
                                "cost": 63.2,
                                "chosen": false
                              },
                              {
                                "access_type": "scan",
                                "cost": 1.13e6,
                                "rows": 5244386,
                                "cause": "cost",
                                "chosen": false
                              }
                            ]
                          },
                          "cost_for_plan": 27.2,
                          "rows_for_plan": 63,
                          "chosen": true
                        }
                      ]
                    },
                    {
                      "plan_prefix": [
                      ],
                      "table": "`sample` `s`",
                      "best_access_path": {
                        "considered_access_paths": [
                          {
                            "access_type": "ref",
                            "index": "PRIMARY",
                            "rows": 1,
                            "cost": 1.2,
                            "chosen": true
                          },
                          {
                            "access_type": "ref",
                            "index": "sample_kind_id",
                            "rows": 1,
                            "cost": 1.4,
                            "chosen": false
                          },
                          {
                            "access_type": "scan",
                            "cost": 1.13e6,
                            "rows": 5244386,
                            "cause": "cost",
                            "chosen": false
                          }
                        ]
                      },
                      "cost_for_plan": 1.2,
                      "rows_for_plan": 1,
                      "rest_of_plan": [
                        {
                          "plan_prefix": [
                            "`sample` `s`"
                          ],
                          "table": "`sample_kind` `sk`",
                          "best_access_path": {
                            "considered_access_paths": [
                              {
                                "access_type": "ref",
                                "index": "PRIMARY",
                                "rows": 1,
                                "cost": 1.2,
                                "chosen": true
                              },
                              {
                                "access_type": "scan",
                                "cost": 13.6,
                                "rows": 63,
                                "cause": "cost",
                                "chosen": false
                              }
                            ]
                          },
                          "added_to_eq_ref_extension": true,
                          "cost_for_plan": 2.4,
                          "rows_for_plan": 1,
                          "chosen": true
                        }
                      ]
                    }
                  ]
                },
                {
                  "attaching_conditions_to_tables": {
                    "original_condition": "((`sk`.`id` = `s`.`sample_kind_id`) and (`s`.`id` = `sa`.`sample_id`))",
                    "attached_conditions_computation": [
                    ],
                    "attached_conditions_summary": [
                      {
                        "table": "`sample` `s`",
                        "attached": null
                      },
                      {
                        "table": "`sample_kind` `sk`",
                        "attached": null
                      }
                    ]
                  }
                },
                {
                  "refine_plan": [
                    {
                      "table": "`sample` `s`"
                    },
                    {
                      "table": "`sample_kind` `sk`"
                    }
                  ]
                }
              ]
            }
          },
          {
            "join_explain": {
              "select#": 2,
              "steps": [
              ]
            }
          }
        ]
      }
    }
  ]
}