SELECT 
  cscart_product_features.status 
FROM 
  cscart_product_features 
  INNER JOIN cscart_product_feature_variants ON cscart_product_features.feature_id = cscart_product_feature_variants.feature_id 
WHERE 
  cscart_product_feature_variants.variant_id = 327

Query time 0.00012

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_product_feature_variants",
          "access_type": "const",
          "possible_keys": ["PRIMARY", "feature_id"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["variant_id"],
          "ref": ["const"],
          "rows": 1,
          "filtered": 100
        }
      },
      {
        "table": {
          "table_name": "cscart_product_features",
          "access_type": "const",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["feature_id"],
          "ref": ["const"],
          "rows": 1,
          "filtered": 100
        }
      }
    ]
  }
}