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 = 271 
WHERE 
  cscart_products_categories.product_id IN (
    6619, 6620, 6621, 6622, 2272, 2273, 2274, 
    2275, 2276, 2340, 2341, 2342, 2343, 
    2344, 2345, 2346, 2347, 2348, 2421, 
    2422, 2423, 2424, 2425, 2426, 2427, 
    2428, 2429, 2430, 2431, 2432, 2433, 
    2434, 2435, 2436, 2437, 2438, 2519, 
    2520, 2521, 2522, 2523, 2524, 2525, 
    2526, 2527, 2608, 2609, 2610, 2611, 
    2612, 2613, 2614, 2615, 2616, 5872, 
    5873, 5874, 5875, 5940, 5941, 5942, 
    5943, 5944, 5945, 5946, 5947, 5948, 
    6021, 6022, 6023, 6024, 6025, 6026, 
    6027, 6028, 6029, 6030, 6031, 6032, 
    6033, 6034, 6035, 6036, 6037, 6038, 
    6111, 6112, 6113, 6114, 6115, 6116, 
    6117, 6118, 6119, 6201, 6202
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00341

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "68.46"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": true,
      "cost_info": {
        "sort_cost": "1.60"
      },
      "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": "0.91",
            "index_condition": "(`gaseus`.`cscart_products_categories`.`product_id` in (6619,6620,6621,6622,2272,2273,2274,2275,2276,2340,2341,2342,2343,2344,2345,2346,2347,2348,2421,2422,2423,2424,2425,2426,2427,2428,2429,2430,2431,2432,2433,2434,2435,2436,2437,2438,2519,2520,2521,2522,2523,2524,2525,2526,2527,2608,2609,2610,2611,2612,2613,2614,2615,2616,5872,5873,5874,5875,5940,5941,5942,5943,5944,5945,5946,5947,5948,6021,6022,6023,6024,6025,6026,6027,6028,6029,6030,6031,6032,6033,6034,6035,6036,6037,6038,6111,6112,6113,6114,6115,6116,6117,6118,6119,6201,6202))",
            "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": "66.86",
              "data_read_per_join": "25"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "position"
            ]
          }
        }
      ]
    }
  }
}