SELECT 
  cscart_products_categories.product_id, 
  GROUP_CONCAT(
    IF(
      cscart_products_categories.link_type = "M", 
      CONCAT(
        cscart_products_categories.category_id, 
        "M"
      ), 
      cscart_products_categories.category_id
    )
  ) AS category_ids 
FROM 
  cscart_products_categories 
  INNER JOIN cscart_categories ON cscart_categories.category_id = cscart_products_categories.category_id 
  AND cscart_categories.storefront_id IN (0, 1) 
  AND (
    cscart_categories.usergroup_ids = '' 
    OR FIND_IN_SET(
      0, cscart_categories.usergroup_ids
    ) 
    OR FIND_IN_SET(
      1, cscart_categories.usergroup_ids
    )
  ) 
  AND cscart_categories.status IN ('A', 'H') 
WHERE 
  cscart_products_categories.product_id IN (
    908, 134, 955, 942, 941, 446, 953, 952, 
    951, 949, 948, 947, 946, 945, 944, 994, 
    996, 493, 985, 986, 988, 990, 991, 993, 
    1128, 1127, 1126, 1125, 1124, 1123, 
    1139, 1138, 1137, 1136, 1135, 1134, 
    1133, 1132, 1131, 1130, 1129, 827, 1142, 
    853, 1146, 1145, 1144, 1143, 856, 1322, 
    1262, 1317, 1318, 1319, 1320, 1321, 
    1256, 1395, 1396, 1397, 1399, 1406, 
    1407, 1408, 1409, 1410, 1411, 1412, 
    1273, 1425, 1427, 1428, 1429, 1431, 
    1266, 1442, 1447, 1263, 1458, 1284, 
    1475, 1476, 1477, 1274, 1483, 1484, 
    1485, 1486, 1487, 1540, 1541, 1542, 
    1543, 1538, 8496, 1517, 8498, 8497, 
    1532, 8502, 8501, 8499, 1528, 8505, 
    8503
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00493

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "251.86"
    },
    "grouping_operation": {
      "using_filesort": false,
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_products_categories",
            "access_type": "range",
            "possible_keys": [
              "PRIMARY",
              "pt"
            ],
            "key": "pt",
            "used_key_parts": [
              "product_id"
            ],
            "key_length": "3",
            "rows_examined_per_scan": 282,
            "rows_produced_per_join": 282,
            "filtered": "100.00",
            "index_condition": "(`softwarepirmam_hewadelivard_cscart_4`.`cscart_products_categories`.`product_id` in (908,134,955,942,941,446,953,952,951,949,948,947,946,945,944,994,996,493,985,986,988,990,991,993,1128,1127,1126,1125,1124,1123,1139,1138,1137,1136,1135,1134,1133,1132,1131,1130,1129,827,1142,853,1146,1145,1144,1143,856,1322,1262,1317,1318,1319,1320,1321,1256,1395,1396,1397,1399,1406,1407,1408,1409,1410,1411,1412,1273,1425,1427,1428,1429,1431,1266,1442,1447,1263,1458,1284,1475,1476,1477,1274,1483,1484,1485,1486,1487,1540,1541,1542,1543,1538,8496,1517,8498,8497,1532,8502,8501,8499,1528,8505,8503))",
            "cost_info": {
              "read_cost": "124.96",
              "eval_cost": "28.20",
              "prefix_cost": "153.16",
              "data_read_per_join": "4K"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "link_type"
            ]
          }
        },
        {
          "table": {
            "table_name": "cscart_categories",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "c_status",
              "p_category_id"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "category_id"
            ],
            "key_length": "3",
            "ref": [
              "softwarepirmam_hewadelivard_cscart_4.cscart_products_categories.category_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 14,
            "filtered": "5.00",
            "cost_info": {
              "read_cost": "70.50",
              "eval_cost": "1.41",
              "prefix_cost": "251.86",
              "data_read_per_join": "44K"
            },
            "used_columns": [
              "category_id",
              "storefront_id",
              "usergroup_ids",
              "status"
            ],
            "attached_condition": "((`softwarepirmam_hewadelivard_cscart_4`.`cscart_categories`.`storefront_id` in (0,1)) and ((`softwarepirmam_hewadelivard_cscart_4`.`cscart_categories`.`usergroup_ids` = '') or (0 <> find_in_set(0,`softwarepirmam_hewadelivard_cscart_4`.`cscart_categories`.`usergroup_ids`)) or (0 <> find_in_set(1,`softwarepirmam_hewadelivard_cscart_4`.`cscart_categories`.`usergroup_ids`))) and (`softwarepirmam_hewadelivard_cscart_4`.`cscart_categories`.`status` in ('A','H')))"
          }
        }
      ]
    }
  }
}