SELECT 
  * 
FROM 
  cscart_product_feature_variants 
WHERE 
  variant_id IN (
    1862, 1143, 524, 3688, 539, 1524, 1527, 
    1526, 1436, 1870, 0
  )

Query time 0.00039

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": 11,
          "filtered": 100,
          "index_condition": "cscart_product_feature_variants.variant_id in (1862,1143,524,3688,539,1524,1527,1526,1436,1870,0)"
        }
      }
    ]
  }
}