mysql> SELECT * FROM INFORMATION_SCHEMA.OPTIMIZER_TRACE\G
*************************** 1. row ***************************
                            QUERY: EXPLAIN UPDATE users, (SELECT 1) dummy SET primary_password = CONCAT('test', 'explain', password) WHERE primary_password IS NULL AND password != '' AND salt IS NOT NULL
                            TRACE: {
  "steps": [
    {
      "join_preparation": {
        "select#": 2,
        "steps": [
          {
            "expanded_query": "/* select#2 */ select 1 AS `1`"
          }
        ]
      }
    },
    {
      "join_preparation": {
        "select#": 1,
        "steps": [
          {
            "expanded_query": "/* select#1 */ select `users`.`primary_password` AS `primary_password` from `users` join (/* select#2 */ select 1 AS `1`) `dummy` where (isnull(`users`.`primary_password`) and (`users`.`password` <> '') and (`users`.`salt` is not null))"
          }
        ]
      }
    },
    {
      "join_optimization": {
        "select#": 1,
        "steps": [
          {
            "join_optimization": {
              "select#": 2,
              "steps": [
              ]
            }
          },
          {
            "creating_tmp_table": {
              "tmp_table_info": {
                "table": " `dummy`",
                "row_length": 5,
                "key_length": 0,
                "unique_constraint": false,
                "location": "memory (heap)",
                "row_limit_estimate": 13421772
              }
            }
          },
          {
            "join_execution": {
              "select#": 2,
              "steps": [
              ]
            }
          },
          {
            "condition_processing": {
              "condition": "WHERE",
              "original_condition": "(isnull(`users`.`primary_password`) and (`users`.`password` <> '') and (`users`.`salt` is not null))",
              "steps": [
                {
                  "transformation": "equality_propagation",
                  "resulting_condition": "(isnull(`users`.`primary_password`) and (`users`.`password` <> '') and (`users`.`salt` is not null))"
                },
                {
                  "transformation": "constant_propagation",
                  "resulting_condition": "(isnull(`users`.`primary_password`) and (`users`.`password` <> '') and (`users`.`salt` is not null))"
                },
                {
                  "transformation": "trivial_condition_removal",
                  "resulting_condition": "(isnull(`users`.`primary_password`) and (`users`.`password` <> '') and (`users`.`salt` is not null))"
                }
              ]
            }
          },
          {
            "table_dependencies": [
              {
                "table": "`users`",
                "row_may_be_null": false,
                "map_bit": 0,
                "depends_on_map_bits": [
                ]
              },
              {
                "table": " `dummy`",
                "row_may_be_null": false,
                "map_bit": 1,
                "depends_on_map_bits": [
                ]
              }
            ]
          },
          {
            "ref_optimizer_key_uses": [
              {
                "table": "`users`",
                "field": "primary_password",
                "equals": "NULL",
                "null_rejecting": false
              }
            ]
          },
          {
            "rows_estimation": [
              {
                "table": "`users`",
                "range_analysis": {
                  "table_scan": {
                    "rows": 92274,
                    "cost": 20976
                  },
                  "potential_range_indices": [
                    {
                      "index": "PRIMARY",
                      "usable": false,
                      "cause": "not_applicable"
                    },
                    {
                      "index": "uniq_email",
                      "usable": false,
                      "cause": "not_applicable"
                    },
                    {
                      "index": "uniq_userName",
                      "usable": false,
                      "cause": "not_applicable"
                    },
                    {
                      "index": "guid",
                      "usable": false,
                      "cause": "not_applicable"
                    },
                    {
                      "index": "password",
                      "usable": true,
                      "key_parts": [
                        "password",
                        "salt",
                        "primary_password",
                        "ID"
                      ]
                    },
                    {
                      "index": "primary_password",
                      "usable": true,
                      "key_parts": [
                        "primary_password",
                        "salt",
                        "password",
                        "ID"
                      ]
                    }
                  ],
                  "setup_range_conditions": [
                  ],
                  "group_index_range": {
                    "chosen": false,
                    "cause": "not_single_table"
                  },
                  "analyzing_range_alternatives": {
                    "range_scan_alternatives": [
                      {
                        "index": "password",
                        "ranges": [
                          "password < ",
                          " < password"
                        ],
                        "index_dives_for_eq_ranges": true,
                        "rowid_ordered": false,
                        "using_mrr": false,
                        "index_only": false,
                        "rows": 46138,
                        "cost": 55368,
                        "chosen": false,
                        "cause": "cost"
                      },
                      {
                        "index": "primary_password",
                        "ranges": [
                          "NULL <= primary_password <= NULL AND NULL < salt"
                        ],
                        "index_dives_for_eq_ranges": true,
                        "rowid_ordered": false,
                        "using_mrr": false,
                        "index_only": false,
                        "rows": 38198,
                        "cost": 45839,
                        "chosen": false,
                        "cause": "cost"
                      }
                    ],
                    "analyzing_roworder_intersect": {
                      "usable": false,
                      "cause": "too_few_roworder_scans"
                    }
                  }
                }
              },
              {
                "table": " `dummy`",
                "rows": 1,
                "cost": 1,
                "table_type": "system",
                "empty": false
              }
            ]
          },
          {
            "considered_execution_plans": [
              {
                "plan_prefix": [
                  " `dummy`"
                ],
                "table": "`users`",
                "best_access_path": {
                  "considered_access_paths": [
                    {
                      "access_type": "ref",
                      "index": "primary_password",
                      "rows": 38198,
                      "cost": 15197,
                      "chosen": true
                    },
                    {
                      "access_type": "scan",
                      "rows": 38198,
                      "cost": 20974,
                      "chosen": false
                    }
                  ]
                },
                "cost_for_plan": 15197,
                "rows_for_plan": 38198,
                "chosen": true
              }
            ]
          },
          {
            "creating_tmp_table": {
              "tmp_table_info": {
                "table": "intermediate_tmp_table",
                "row_length": 106,
                "key_length": 4,
                "unique_constraint": false,
                "location": "memory (heap)",
                "row_limit_estimate": 633102
              }
            }
          },
          {
            "attaching_conditions_to_tables": {
              "original_condition": "(isnull(`users`.`primary_password`) and (`users`.`password` <> '') and (`users`.`salt` is not null))",
              "attached_conditions_computation": [
              ],
              "attached_conditions_summary": [
                {
                  "table": "`users`",
                  "attached": "(isnull(`users`.`primary_password`) and (`users`.`password` <> '') and (`users`.`salt` is not null))"
                }
              ]
            }
          },
          {
            "refine_plan": [
              {
                "table": "`users`"
              }
            ]
          }
        ]
      }
    },
    {
      "join_explain": {
        "select#": 1,
        "steps": [
          {
            "join_explain": {
              "select#": 2,
              "steps": [
              ]
            }
          }
        ]
      }
    }
  ]
}
MISSING_BYTES_BEYOND_MAX_MEM_SIZE: 0
          INSUFFICIENT_PRIVILEGES: 0
1 row in set (0.00 sec)