SELECT 
  * 
FROM 
  cscart_product_feature_variants 
WHERE 
  variant_id IN (
    1449, 1201, 1219, 5899, 1283, 1257, 5902, 
    5904, 5905, 5907, 5908, 1282, 1425, 
    1280, 1200, 5912, 1198, 1199, 1241, 
    5916, 5942
  )

Query time 0.00042

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_product_feature_variants",
      "access_type": "range",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "3",
      "used_key_parts": ["variant_id"],
      "rows": 21,
      "filtered": 100,
      "index_condition": "cscart_product_feature_variants.variant_id in (1449,1201,1219,5899,1283,1257,5902,5904,5905,5907,5908,1282,1425,1280,1200,5912,1198,1199,1241,5916,5942)"
    }
  }
}