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 (
    276426, 276427, 276428, 276429, 276430, 
    276431, 276432, 276433, 276434, 276435, 
    276436, 276437, 276438, 276439, 276440, 
    276441, 276442, 276443, 276444, 276445, 
    276446, 276447, 276448, 276449, 276450, 
    276451, 276452, 276453, 276454, 276455, 
    276456, 276457, 276458, 276459, 276460, 
    276461, 276462, 276463, 276464, 276465, 
    276466, 276467, 276468, 276469, 276470, 
    276471, 276472, 276473, 276474, 276475, 
    276476, 276477, 276478, 276497, 276498, 
    276499, 276500, 276501, 276502, 276503, 
    276504, 276505, 276506, 276507, 276508, 
    276509, 276510, 276511, 276512, 276513, 
    276514, 276515, 276516, 276517, 276518, 
    276519, 276520, 276521, 276522, 276523, 
    276524, 276525, 276526, 276527, 276528, 
    276529, 276530, 276531, 276532, 276533, 
    276534, 276535, 276536, 276537, 276538, 
    276539, 276540
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00241

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "101.86"
    },
    "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": 97,
            "rows_produced_per_join": 97,
            "filtered": "100.00",
            "index_condition": "(`s2cart`.`cscart_products_categories`.`product_id` in (276426,276427,276428,276429,276430,276431,276432,276433,276434,276435,276436,276437,276438,276439,276440,276441,276442,276443,276444,276445,276446,276447,276448,276449,276450,276451,276452,276453,276454,276455,276456,276457,276458,276459,276460,276461,276462,276463,276464,276465,276466,276467,276468,276469,276470,276471,276472,276473,276474,276475,276476,276477,276478,276497,276498,276499,276500,276501,276502,276503,276504,276505,276506,276507,276508,276509,276510,276511,276512,276513,276514,276515,276516,276517,276518,276519,276520,276521,276522,276523,276524,276525,276526,276527,276528,276529,276530,276531,276532,276533,276534,276535,276536,276537,276538,276539,276540))",
            "cost_info": {
              "read_cost": "58.21",
              "eval_cost": "9.70",
              "prefix_cost": "67.91",
              "data_read_per_join": "1K"
            },
            "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": [
              "s2cart.cscart_products_categories.category_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 4,
            "filtered": "5.00",
            "cost_info": {
              "read_cost": "24.25",
              "eval_cost": "0.49",
              "prefix_cost": "101.86",
              "data_read_per_join": "17K"
            },
            "used_columns": [
              "category_id",
              "usergroup_ids",
              "status",
              "storefront_id"
            ],
            "attached_condition": "((`s2cart`.`cscart_categories`.`storefront_id` in (0,1)) and ((`s2cart`.`cscart_categories`.`usergroup_ids` = '') or (0 <> find_in_set(0,`s2cart`.`cscart_categories`.`usergroup_ids`)) or (0 <> find_in_set(1,`s2cart`.`cscart_categories`.`usergroup_ids`))) and (`s2cart`.`cscart_categories`.`status` in ('A','H')))"
          }
        }
      ]
    }
  }
}