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 = 265 
WHERE 
  cscart_products_categories.product_id IN (
    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, 1626, 
    2281, 2282, 2283, 2284, 2285, 2331, 
    2332, 2333, 2334, 2335, 2403, 2404, 
    2405, 2406, 2407, 2408, 2409, 2410, 
    2411, 2599, 2600, 2601, 2602, 5881, 
    5882, 5883, 5884, 5931, 5932, 5933, 
    5934, 6003, 6004, 6005, 6006, 6007, 
    6008, 6009, 6010, 6011, 6192, 6193, 
    6194, 6195, 2595, 2596, 2597
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00263

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "68.50"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": true,
      "cost_info": {
        "sort_cost": "1.63"
      },
      "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": "0.93",
            "index_condition": "(`gaseus`.`cscart_products_categories`.`product_id` in (2280,2327,2328,2329,2330,2394,2395,2396,2397,2398,2399,2400,2401,2402,2505,2506,2507,2508,5876,5877,5878,5879,5880,5926,5927,5928,5929,5930,5994,5995,5996,5997,5998,5999,6000,6001,6002,6105,6106,6107,6108,1653,2224,1599,1572,2603,6191,2509,1626,2281,2282,2283,2284,2285,2331,2332,2333,2334,2335,2403,2404,2405,2406,2407,2408,2409,2410,2411,2599,2600,2601,2602,5881,5882,5883,5884,5931,5932,5933,5934,6003,6004,6005,6006,6007,6008,6009,6010,6011,6192,6193,6194,6195,2595,2596,2597))",
            "cost_info": {
              "read_cost": "44.00",
              "eval_cost": "0.16",
              "prefix_cost": "66.30",
              "data_read_per_join": "26"
            },
            "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": "0.41",
              "eval_cost": "0.16",
              "prefix_cost": "66.87",
              "data_read_per_join": "26"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "position"
            ]
          }
        }
      ]
    }
  }
}