SELECT 
  v.variant_id, 
  v.product_id, 
  vd.variant, 
  vf.position, 
  vf.color 
FROM 
  cscart_product_features_values v 
  LEFT JOIN cscart_product_feature_variant_descriptions vd ON v.variant_id = vd.variant_id 
  AND vd.lang_code = 'en' 
  LEFT JOIN cscart_product_feature_variants vf ON v.variant_id = vf.variant_id 
WHERE 
  1 
  AND v.feature_id = 1071 
  AND v.product_id IN (
    '29745', '29752', '29751', '29750', 
    '29749', '29748', '29747', '29746', 
    '29744', '29743', '29742', '29741', 
    '29740', '29739', '29738', '29737', 
    '29736', '26629'
  )

Query time 0.00124

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "16.63"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "v",
          "access_type": "range",
          "possible_keys": [
            "PRIMARY",
            "fl",
            "product_id",
            "fpl",
            "idx_product_feature_variant_id"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "feature_id",
            "product_id"
          ],
          "key_length": "6",
          "rows_examined_per_scan": 18,
          "rows_produced_per_join": 18,
          "filtered": "100.00",
          "using_index": true,
          "cost_info": {
            "read_cost": "2.23",
            "eval_cost": "1.80",
            "prefix_cost": "4.03",
            "data_read_per_join": "13K"
          },
          "used_columns": [
            "feature_id",
            "product_id",
            "variant_id"
          ],
          "attached_condition": "((`cscartdb`.`v`.`feature_id` = 1071) and (`cscartdb`.`v`.`product_id` in ('29745','29752','29751','29750','29749','29748','29747','29746','29744','29743','29742','29741','29740','29739','29738','29737','29736','26629')))"
        }
      },
      {
        "table": {
          "table_name": "vd",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "variant_id",
            "lang_code"
          ],
          "key_length": "9",
          "ref": [
            "cscartdb.v.variant_id",
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 18,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "4.50",
            "eval_cost": "1.80",
            "prefix_cost": "10.33",
            "data_read_per_join": "54K"
          },
          "used_columns": [
            "variant_id",
            "variant",
            "lang_code"
          ]
        }
      },
      {
        "table": {
          "table_name": "vf",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "variant_id"
          ],
          "key_length": "3",
          "ref": [
            "cscartdb.v.variant_id"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 18,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "4.50",
            "eval_cost": "1.80",
            "prefix_cost": "16.63",
            "data_read_per_join": "20K"
          },
          "used_columns": [
            "variant_id",
            "color",
            "position"
          ]
        }
      }
    ]
  }
}