SELECT 
  pfv.variant_id, 
  pfv.position, 
  pfvd.variant 
FROM 
  cscart_product_feature_variants AS pfv 
  INNER JOIN cscart_product_feature_variant_descriptions AS pfvd ON pfv.variant_id = pfvd.variant_id 
  AND pfvd.lang_code = 'vi' 
WHERE 
  pfv.variant_id IN (
    81621, 81601, 81609, 81608, 81607, 81606, 
    81605, 81604, 81603, 81602, 81617, 
    81616, 81615, 81614, 81613, 81612, 
    81611, 81610, 81622, 81623, 81624, 
    81625, 87055, 87064, 87065, 87057, 
    87056, 87054, 87063, 87058, 87059, 
    87060, 87061, 87062, 87066, 87076, 
    87077, 87067, 87068, 87069, 87070, 
    87071, 87072, 87073, 87090, 87088, 
    87087, 87089, 87117, 87115, 87118, 
    87119, 87120, 87116, 87121
  )

Query time 0.00150

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "pfv",
          "access_type": "range",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["variant_id"],
          "rows": 55,
          "filtered": 100,
          "index_condition": "pfv.variant_id in (81621,81601,81609,81608,81607,81606,81605,81604,81603,81602,81617,81616,81615,81614,81613,81612,81611,81610,81622,81623,81624,81625,87055,87064,87065,87057,87056,87054,87063,87058,87059,87060,87061,87062,87066,87076,87077,87067,87068,87069,87070,87071,87072,87073,87090,87088,87087,87089,87117,87115,87118,87119,87120,87116,87121)"
        }
      },
      {
        "table": {
          "table_name": "pfvd",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "9",
          "used_key_parts": ["variant_id", "lang_code"],
          "ref": ["dev_db.pfv.variant_id", "const"],
          "rows": 1,
          "filtered": 100,
          "index_condition": "pfvd.lang_code = 'vi'"
        }
      }
    ]
  }
}