SELECT 
  * 
FROM 
  cscart_product_feature_variants 
WHERE 
  variant_id IN (
    3709, 1858, 1862, 1882, 1855, 1878, 2230, 
    1910, 2128, 3101, 3104, 3095, 1313, 
    1856, 1870, 1859, 0
  )

Query time 0.00047

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_product_feature_variants",
          "access_type": "range",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["variant_id"],
          "rows": 17,
          "filtered": 100,
          "index_condition": "cscart_product_feature_variants.variant_id in (3709,1858,1862,1882,1855,1878,2230,1910,2128,3101,3104,3095,1313,1856,1870,1859,0)"
        }
      }
    ]
  }
}