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 = 'en' 
WHERE 
  pfv.variant_id IN (
    12768, 12770, 12772, 12773, 12775, 12777, 
    12779, 12788, 12790, 12792, 12794, 
    12796, 12798, 12800, 12782, 12802, 
    12804, 12806, 12808, 12810, 12812
  )

Query time 0.00028

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.06264255,
    "nested_loop": [
      {
        "table": {
          "table_name": "pfv",
          "access_type": "range",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["variant_id"],
          "loops": 1,
          "rows": 21,
          "cost": 0.03730571,
          "filtered": 100,
          "attached_condition": "pfv.variant_id in (12768,12770,12772,12773,12775,12777,12779,12788,12790,12792,12794,12796,12798,12800,12782,12802,12804,12806,12808,12810,12812)"
        }
      },
      {
        "table": {
          "table_name": "pfvd",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "9",
          "used_key_parts": ["variant_id", "lang_code"],
          "ref": ["u508912950_dev_2025.pfv.variant_id", "const"],
          "loops": 21,
          "rows": 1,
          "cost": 0.02533684,
          "filtered": 100,
          "attached_condition": "pfvd.lang_code = 'en'"
        }
      }
    ]
  }
}