[MariaDB [virtualsheetmusic]> explain format=json select a.* from HLAsset a where a.excluded=0 AND a.date_deleted='' AND a.filetype='SCORCH' AND EXISTS (SELECT 1 FROM HLAssetCategory WHERE asset_id = a.asset_id);
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| EXPLAIN                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
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| {
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "a",
      "access_type": "ref",
      "possible_keys": ["covering"],
      "key": "covering",
      "key_length": "103",
      "used_key_parts": ["excluded", "date_deleted", "filetype"],
      "ref": ["const", "const", "const"],
      "rows": 149991,
      "filtered": 100,
      "index_condition": "a.date_deleted = '' and a.filetype = 'SCORCH'"
    },
    "table": {
      "table_name": "<subquery2>",
      "access_type": "eq_ref",
      "possible_keys": ["distinct_key"],
      "key": "distinct_key",
      "key_length": "35",
      "used_key_parts": ["asset_id"],
      "ref": ["func"],
      "rows": 1,
      "filtered": 100,
      "materialized": {
        "unique": 1,
        "query_block": {
          "select_id": 2,
          "table": {
            "table_name": "HLAssetCategory",
            "access_type": "index",
            "possible_keys": ["PRIMARY"],
            "key": "PRIMARY",
            "key_length": "38",
            "used_key_parts": ["asset_id", "category_id"],
            "rows": 625536,
            "filtered": 100,
            "using_index": true
          }
        }
      }
    }
  }
} |
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1 row in set (0.004 sec)