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SELECT 
  pfv.feature_id, 
  pfv.product_id, 
  pfv.variant_id, 
  gp.group_id 
FROM 
  cscart_product_features_values AS pfv 
  INNER JOIN cscart_product_variation_group_products AS gp ON pfv.product_id = gp.product_id 
  INNER JOIN cscart_product_variation_group_features AS gpf ON gpf.group_id = gp.group_id 
  AND gpf.feature_id = pfv.feature_id 
WHERE 
  pfv.lang_code = 'en' 
  AND gp.group_id IN (1063)

Query time 0.00129

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "193.98"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "gpf",
          "access_type": "ref",
          "possible_keys": [
            "PRIMARY",
            "idx_group_id"
          ],
          "key": "idx_group_id",
          "used_key_parts": [
            "group_id"
          ],
          "key_length": "3",
          "ref": [
            "const"
          ],
          "rows_examined_per_scan": 3,
          "rows_produced_per_join": 3,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "0.75",
            "eval_cost": "0.30",
            "prefix_cost": "1.05",
            "data_read_per_join": "312"
          },
          "used_columns": [
            "feature_id",
            "group_id"
          ]
        }
      },
      {
        "table": {
          "table_name": "gp",
          "access_type": "ref",
          "possible_keys": [
            "PRIMARY",
            "idx_group_id"
          ],
          "key": "idx_group_id",
          "used_key_parts": [
            "group_id"
          ],
          "key_length": "3",
          "ref": [
            "const"
          ],
          "rows_examined_per_scan": 59,
          "rows_produced_per_join": 177,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "21.72",
            "eval_cost": "17.70",
            "prefix_cost": "40.47",
            "data_read_per_join": "2K"
          },
          "used_columns": [
            "product_id",
            "group_id"
          ]
        }
      },
      {
        "table": {
          "table_name": "pfv",
          "access_type": "ref",
          "possible_keys": [
            "PRIMARY",
            "lang_code",
            "product_id",
            "fpl",
            "idx_product_feature_variant_id",
            "fl"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "feature_id",
            "product_id"
          ],
          "key_length": "6",
          "ref": [
            "cscart_db.gpf.feature_id",
            "cscart_db.gp.product_id"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 103,
          "filtered": "50.00",
          "using_index": true,
          "cost_info": {
            "read_cost": "132.86",
            "eval_cost": "10.33",
            "prefix_cost": "193.98",
            "data_read_per_join": "4K"
          },
          "used_columns": [
            "feature_id",
            "product_id",
            "variant_id",
            "lang_code"
          ],
          "attached_condition": "(`cscart_db`.`pfv`.`lang_code` = 'en')"
        }
      }
    ]
  }
}

Result

feature_id	product_id	variant_id	group_id
63	66749	10351	1063
63	66748	10351	1063
63	66743	10351	1063
63	66747	10351	1063
63	66756	10351	1063
63	66746	10351	1063
63	66745	10351	1063
63	66744	10351	1063
63	66742	10351	1063
63	66775	10351	1063
63	66776	10351	1063
63	66777	10351	1063
63	66778	10351	1063
63	66779	10351	1063
63	66780	10351	1063
63	66781	10351	1063
63	66740	10351	1063
63	66739	10351	1063
63	66738	10351	1063
63	66737	10351	1063
63	66736	10351	1063
63	66735	10351	1063
63	66734	10351	1063
63	66733	10351	1063
63	66732	10351	1063
63	66731	10351	1063
63	66730	10351	1063
63	66729	10351	1063
63	66741	10351	1063
63	66728	10351	1063
63	66773	10351	1063
63	66770	10351	1063
63	66769	10351	1063
63	66771	10351	1063
63	66768	10351	1063
63	66767	10351	1063
63	66766	10351	1063
63	66765	10351	1063
63	66763	10351	1063
63	66762	10351	1063
63	66764	10351	1063
63	66761	10351	1063
63	66760	10351	1063
63	66772	10351	1063
63	66727	10351	1063
63	66757	10351	1063
63	66759	10351	1063
63	66785	10351	1063
63	66784	10351	1063
63	66774	10351	1063
63	66758	10351	1063
63	66786	10351	1063
63	66755	10351	1063
63	66754	10351	1063
63	66753	10351	1063
63	66752	10351	1063
63	66751	10351	1063
63	66750	10351	1063
63	66783	10351	1063
63	66782	10351	1063
104	66749	62350	1063
104	66748	62349	1063
104	66743	62347	1063
104	66747	62349	1063
104	66756	62354	1063
104	66746	62348	1063
104	66745	62348	1063
104	66744	62347	1063
104	66742	62346	1063
104	66775	62362	1063
104	66776	62362	1063
104	66777	62363	1063
104	66778	62363	1063
104	66779	62052	1063
104	66780	62052	1063
104	66781	62364	1063
104	66740	62345	1063
104	66739	62345	1063
104	66738	62344	1063
104	66737	62344	1063
104	66736	62343	1063
104	66735	62343	1063
104	66734	62342	1063
104	66733	62342	1063
104	66732	62341	1063
104	66731	62341	1063
104	66730	62340	1063
104	66729	62340	1063
104	66741	62346	1063
104	66728	62339	1063
104	66773	62361	1063
104	66770	62359	1063
104	66769	62359	1063
104	66771	62360	1063
104	66768	62054	1063
104	66767	62054	1063
104	66766	62053	1063
104	66765	62053	1063
104	66763	62358	1063
104	66762	62357	1063
104	66764	62358	1063
104	66761	62357	1063
104	66760	62356	1063
104	66772	62360	1063
104	66727	62339	1063
104	66757	62355	1063
104	66759	62356	1063
104	66785	62366	1063
104	66784	62365	1063
104	66774	62361	1063
104	66758	62051	1063
104	66786	62366	1063
104	66755	62354	1063
104	66754	62353	1063
104	66753	62352	1063
104	66752	62351	1063
104	66751	62351	1063
104	66750	62350	1063
104	66783	62365	1063
104	66782	62364	1063
67	66749	41509	1063
67	66748	19983	1063
67	66743	41509	1063
67	66747	41509	1063
67	66756	19983	1063
67	66746	19983	1063
67	66745	41509	1063
67	66744	19983	1063
67	66742	19983	1063
67	66775	41509	1063
67	66776	19983	1063
67	66777	41509	1063
67	66778	19983	1063
67	66779	41509	1063
67	66780	19983	1063
67	66781	41509	1063
67	66740	19983	1063
67	66739	41509	1063
67	66738	19983	1063
67	66737	41509	1063
67	66736	19983	1063
67	66735	41509	1063
67	66734	19983	1063
67	66733	41509	1063
67	66732	19983	1063
67	66731	41509	1063
67	66730	19983	1063
67	66729	41509	1063
67	66741	41509	1063
67	66728	19983	1063
67	66773	41509	1063
67	66770	19983	1063
67	66769	41509	1063
67	66771	41509	1063
67	66768	19983	1063
67	66767	41509	1063
67	66766	19983	1063
67	66765	41509	1063
67	66763	41509	1063
67	66762	19983	1063
67	66764	19983	1063
67	66761	41509	1063
67	66760	19983	1063
67	66772	19983	1063
67	66727	41509	1063
67	66757	41509	1063
67	66759	41509	1063
67	66785	41509	1063
67	66784	19983	1063
67	66774	19983	1063
67	66758	19983	1063
67	66786	19983	1063
67	66755	41509	1063
67	66754	19983	1063
67	66753	41509	1063
67	66752	19983	1063
67	66751	41509	1063
67	66750	19983	1063
67	66783	41509	1063
67	66782	19983	1063