analyze format=json select * from t1,t1_subsets where t1.subset_id IS NOT NULL and t1.subset_id= t1_subsets.id;

ANALYZE

{

  "query_block": {

    "select_id": 1,

    "r_loops": 1,

    "r_total_time_ms": 0.0594,

    "table": {

      "table_name": "t1",

      "access_type": "range",

      "possible_keys": ["t1_subset_id"],

      "key": "t1_subset_id",

      "key_length": "5",

      "used_key_parts": ["subset_id"],

      "r_loops": 1,

      "rows": 3,

      "r_rows": 0,

      "r_total_time_ms": 0.0226,

      "filtered": 100,

      "r_filtered": 100,

      "index_condition": "((t1.subset_id is not null) and (t1.subset_id is not null))"

    },

    "table": {

      "table_name": "t1_subsets",

      "access_type": "eq_ref",

      "possible_keys": ["PRIMARY"],

      "key": "PRIMARY",

      "key_length": "4",

      "used_key_parts": ["id"],

      "ref": ["test.t1.subset_id"],

      "r_loops": 0,

      "rows": 1,

      "r_rows": null,

      "filtered": 100,

      "r_filtered": null,

      "index_condition": "(t1.subset_id = t1_subsets.`id`)"

    }

  }

}