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 = 87

Query time 0.00011

JSON explain

{
  "query_block": {
    "select_id": 1,
    "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
    }
  }
}