SELECT 
  pfv.feature_id, 
  pfv.product_id, 
  pfv.variant_id, 
  fv.position, 
  fvd.variant 
FROM 
  cscart_product_features_values AS pfv 
  INNER JOIN cscart_product_feature_variants AS fv ON pfv.feature_id = fv.feature_id 
  AND pfv.variant_id = fv.variant_id 
  INNER JOIN cscart_product_feature_variant_descriptions AS fvd ON pfv.variant_id = fvd.variant_id 
  AND fvd.lang_code = 'en' 
WHERE 
  pfv.feature_id IN (643, 656, 648, 766, 649) 
  AND pfv.product_id IN (
    1274, 1406, 1266, 1428, 1263, 1256, 1319, 
    1273, 4526, 1532, 4796, 8499, 8502, 
    8501, 4798, 1284, 1528, 4767, 1517, 
    1542, 4744, 8498, 8497, 1540, 1544, 
    4812, 1538, 8503, 8505, 8496, 10136, 
    10137, 5774
  ) 
  AND pfv.lang_code = 'en'

Query time 0.00540

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "98.76"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "pfv",
          "access_type": "range",
          "possible_keys": [
            "PRIMARY",
            "fl",
            "variant_id",
            "lang_code",
            "product_id",
            "fpl",
            "idx_product_feature_variant_id"
          ],
          "key": "idx_product_feature_variant_id",
          "used_key_parts": [
            "product_id",
            "feature_id",
            "lang_code"
          ],
          "key_length": "12",
          "rows_examined_per_scan": 168,
          "rows_produced_per_join": 168,
          "filtered": "100.00",
          "using_index": true,
          "cost_info": {
            "read_cost": "18.73",
            "eval_cost": "16.80",
            "prefix_cost": "35.53",
            "data_read_per_join": "129K"
          },
          "used_columns": [
            "feature_id",
            "product_id",
            "variant_id",
            "lang_code"
          ],
          "attached_condition": "((`softwarepirmam_hewadelivard_cscart_4`.`pfv`.`feature_id` in (643,656,648,766,649)) and (`softwarepirmam_hewadelivard_cscart_4`.`pfv`.`product_id` in (1274,1406,1266,1428,1263,1256,1319,1273,4526,1532,4796,8499,8502,8501,4798,1284,1528,4767,1517,1542,4744,8498,8497,1540,1544,4812,1538,8503,8505,8496,10136,10137,5774)) and (`softwarepirmam_hewadelivard_cscart_4`.`pfv`.`lang_code` = 'en'))"
        }
      },
      {
        "table": {
          "table_name": "fv",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY",
            "feature_id"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "variant_id"
          ],
          "key_length": "3",
          "ref": [
            "softwarepirmam_hewadelivard_cscart_4.pfv.variant_id"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 12,
          "filtered": "7.54",
          "cost_info": {
            "read_cost": "42.00",
            "eval_cost": "1.27",
            "prefix_cost": "94.33",
            "data_read_per_join": "14K"
          },
          "used_columns": [
            "variant_id",
            "feature_id",
            "position"
          ],
          "attached_condition": "(`softwarepirmam_hewadelivard_cscart_4`.`fv`.`feature_id` = `softwarepirmam_hewadelivard_cscart_4`.`pfv`.`feature_id`)"
        }
      },
      {
        "table": {
          "table_name": "fvd",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "variant_id",
            "lang_code"
          ],
          "key_length": "9",
          "ref": [
            "softwarepirmam_hewadelivard_cscart_4.pfv.variant_id",
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 12,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "3.17",
            "eval_cost": "1.27",
            "prefix_cost": "98.76",
            "data_read_per_join": "38K"
          },
          "used_columns": [
            "variant_id",
            "variant",
            "lang_code"
          ]
        }
      }
    ]
  }
}