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, 
  product_position_source.position AS position 
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') 
  LEFT JOIN cscart_products_categories AS product_position_source ON cscart_products_categories.product_id = product_position_source.product_id 
  AND product_position_source.category_id = 308 
WHERE 
  cscart_products_categories.product_id IN (
    2760, 2761, 2762, 2763, 2764, 6348, 6349, 
    6350, 6351, 2756, 2757, 2758, 2759, 
    6343, 6344, 6345, 6346, 6347, 2818, 
    2819, 2820, 2821, 2822, 6404, 6405, 
    6406, 6407, 2933, 2934, 2935, 2936, 
    6517, 6518, 6519, 6520, 6521, 2510, 
    2511, 2512, 2513, 3837, 3838, 3839, 
    6109, 6110, 2277, 2278, 2279, 2280, 
    2327, 2328, 2329, 2330, 2394, 2395, 
    2396, 2397, 2398, 2399, 2400, 2401, 
    2402, 2505, 2506, 2507, 2508, 5876, 
    5877, 5878, 5879, 5880, 5926, 5927, 
    5928, 5929, 5930, 5994, 5995, 5996, 
    5997, 5998, 5999, 6000, 6001, 6002, 
    6105, 6106, 6107, 6108, 1653, 2224, 
    1599, 1572, 2603, 6191, 2509
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00327

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "68.48"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": true,
      "cost_info": {
        "sort_cost": "1.61"
      },
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_categories",
            "access_type": "ALL",
            "possible_keys": [
              "PRIMARY",
              "c_status",
              "p_category_id"
            ],
            "rows_examined_per_scan": 40,
            "rows_produced_per_join": 1,
            "filtered": "4.00",
            "cost_info": {
              "read_cost": "4.54",
              "eval_cost": "0.16",
              "prefix_cost": "4.70",
              "data_read_per_join": "6K"
            },
            "used_columns": [
              "category_id",
              "storefront_id",
              "usergroup_ids",
              "status"
            ],
            "attached_condition": "((`gaseus`.`cscart_categories`.`storefront_id` in (0,1)) and ((`gaseus`.`cscart_categories`.`usergroup_ids` = '') or (0 <> find_in_set(0,`gaseus`.`cscart_categories`.`usergroup_ids`)) or (0 <> find_in_set(1,`gaseus`.`cscart_categories`.`usergroup_ids`))) and (`gaseus`.`cscart_categories`.`status` in ('A','H')))"
          }
        },
        {
          "table": {
            "table_name": "cscart_products_categories",
            "access_type": "ref",
            "possible_keys": [
              "PRIMARY",
              "pt"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "category_id"
            ],
            "key_length": "3",
            "ref": [
              "gaseus.cscart_categories.category_id"
            ],
            "rows_examined_per_scan": 110,
            "rows_produced_per_join": 1,
            "filtered": "0.92",
            "index_condition": "(`gaseus`.`cscart_products_categories`.`product_id` in (2760,2761,2762,2763,2764,6348,6349,6350,6351,2756,2757,2758,2759,6343,6344,6345,6346,6347,2818,2819,2820,2821,2822,6404,6405,6406,6407,2933,2934,2935,2936,6517,6518,6519,6520,6521,2510,2511,2512,2513,3837,3838,3839,6109,6110,2277,2278,2279,2280,2327,2328,2329,2330,2394,2395,2396,2397,2398,2399,2400,2401,2402,2505,2506,2507,2508,5876,5877,5878,5879,5880,5926,5927,5928,5929,5930,5994,5995,5996,5997,5998,5999,6000,6001,6002,6105,6106,6107,6108,1653,2224,1599,1572,2603,6191,2509))",
            "cost_info": {
              "read_cost": "44.00",
              "eval_cost": "0.16",
              "prefix_cost": "66.30",
              "data_read_per_join": "25"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "link_type"
            ]
          }
        },
        {
          "table": {
            "table_name": "product_position_source",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "pt"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "category_id",
              "product_id"
            ],
            "key_length": "6",
            "ref": [
              "const",
              "gaseus.cscart_products_categories.product_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 1,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "0.40",
              "eval_cost": "0.16",
              "prefix_cost": "66.87",
              "data_read_per_join": "25"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "position"
            ]
          }
        }
      ]
    }
  }
}