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 (
    68839, 68838, 68837, 68836, 68840, 72194, 
    72193, 73313, 73312, 73315, 73314, 
    73527, 73526, 78278, 78277, 78280, 
    78483, 78484, 79632, 79633, 79634, 
    79635, 79644, 79645, 84336, 84335
  )

Query time 0.01031

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": 26,
          "filtered": 100,
          "index_condition": "pfv.variant_id in (68839,68838,68837,68836,68840,72194,72193,73313,73312,73315,73314,73527,73526,78278,78277,78280,78483,78484,79632,79633,79634,79635,79644,79645,84336,84335)"
        }
      },
      {
        "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'"
        }
      }
    ]
  }
}