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 (
    3863, 3148, 6718, 6722, 3144, 3147, 3096, 
    339, 3104, 3107, 6682, 6678, 104, 105, 
    106, 107, 108, 109, 110, 4013, 4014, 
    4015, 4016, 4017, 4018, 4019, 3105, 
    6677, 6686, 64, 118, 224, 225, 285, 3975, 
    4027, 4108, 4109, 4170, 4223, 203, 204, 
    205, 206, 207, 208, 209, 4087, 4088, 
    4089, 4090, 4091, 4092, 4093, 3122, 
    6675, 6696, 6703, 3118, 3111, 3124, 
    3112, 324, 3419, 6704, 3418, 6709, 6946, 
    4177, 6945, 338, 331, 6705, 3932, 3134, 
    3116, 3126, 6673, 6679, 6691, 3155, 
    3131, 310, 303, 3939, 317, 3132, 3143, 
    3130, 3129, 3121, 3128, 6681, 6695, 
    3098, 3115
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00278

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 (3863,3148,6718,6722,3144,3147,3096,339,3104,3107,6682,6678,104,105,106,107,108,109,110,4013,4014,4015,4016,4017,4018,4019,3105,6677,6686,64,118,224,225,285,3975,4027,4108,4109,4170,4223,203,204,205,206,207,208,209,4087,4088,4089,4090,4091,4092,4093,3122,6675,6696,6703,3118,3111,3124,3112,324,3419,6704,3418,6709,6946,4177,6945,338,331,6705,3932,3134,3116,3126,6673,6679,6691,3155,3131,310,303,3939,317,3132,3143,3130,3129,3121,3128,6681,6695,3098,3115))",
            "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"
            ]
          }
        }
      ]
    }
  }
}