SELECT 
  * 
FROM 
  cscart_product_feature_variants 
WHERE 
  variant_id IN (
    1855, 1930, 1831, 135, 58, 605, 1351, 
    473, 125, 50, 88, 123, 59, 47, 474, 654, 
    422, 1832, 64, 129, 1856, 1870, 0, 1, 
    590, 1808, 121, 341, 637
  )

Query time 0.00054

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": 29,
          "filtered": 100,
          "index_condition": "cscart_product_feature_variants.variant_id in (1855,1930,1831,135,58,605,1351,473,125,50,88,123,59,47,474,654,422,1832,64,129,1856,1870,0,1,590,1808,121,341,637)"
        }
      }
    ]
  }
}