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 (
    12819, 12821, 12823, 12825, 12827, 12829, 
    12831, 12833, 12835, 12837, 12839, 
    12841, 12843, 12845, 12847, 12849, 
    12851, 12853, 12854, 12856, 12858, 
    12860, 12862, 12864, 12866, 12868, 
    12870, 12872, 12873, 12875, 12877, 
    12879, 12881, 12883, 12885, 12887, 
    12889, 12891, 12893, 12895, 12897, 
    12899, 12901, 12903, 12905, 12907, 
    12909, 12911, 12913, 12915
  )

Query time 0.00040

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.13900622,
    "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": 50,
          "cost": 0.08773062,
          "filtered": 100,
          "attached_condition": "pfv.variant_id in (12819,12821,12823,12825,12827,12829,12831,12833,12835,12837,12839,12841,12843,12845,12847,12849,12851,12853,12854,12856,12858,12860,12862,12864,12866,12868,12870,12872,12873,12875,12877,12879,12881,12883,12885,12887,12889,12891,12893,12895,12897,12899,12901,12903,12905,12907,12909,12911,12913,12915)"
        }
      },
      {
        "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": 50,
          "rows": 1,
          "cost": 0.0512756,
          "filtered": 100,
          "attached_condition": "pfvd.lang_code = 'en'"
        }
      }
    ]
  }
}