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 (
    12505, 13099, 12514, 12513, 9759, 10496, 
    10560, 10561, 10581, 10102, 9940, 10578, 
    10143, 9947, 10567, 10568, 10565, 9933, 
    12499, 12500, 10200, 10201, 10566, 
    10545, 10227, 10552, 12506, 10693, 
    12508, 9953, 12522, 12507, 12498, 13101, 
    13100, 10699, 10695, 10195, 10576, 
    10696, 9760, 10583, 10701, 10582, 10139, 
    12503, 10575, 9932, 10075, 10135, 9952, 
    10074, 10573, 10577, 10651, 10642, 
    12529, 12515, 12525, 12532, 12523, 
    10198, 10557, 10202
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00325

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_products_categories",
      "access_type": "range",
      "possible_keys": ["PRIMARY", "pt"],
      "key": "pt",
      "key_length": "3",
      "used_key_parts": ["product_id"],
      "rows": 64,
      "filtered": 100,
      "index_condition": "cscart_products_categories.product_id in (12505,13099,12514,12513,9759,10496,10560,10561,10581,10102,9940,10578,10143,9947,10567,10568,10565,9933,12499,12500,10200,10201,10566,10545,10227,10552,12506,10693,12508,9953,12522,12507,12498,13101,13100,10699,10695,10195,10576,10696,9760,10583,10701,10582,10139,12503,10575,9932,10075,10135,9952,10074,10573,10577,10651,10642,12529,12515,12525,12532,12523,10198,10557,10202)"
    },
    "table": {
      "table_name": "product_position_source",
      "access_type": "eq_ref",
      "possible_keys": ["PRIMARY", "pt"],
      "key": "PRIMARY",
      "key_length": "6",
      "used_key_parts": ["category_id", "product_id"],
      "ref": [
        "const",
        "noframes_angrybeaver.cscart_products_categories.product_id"
      ],
      "rows": 1,
      "filtered": 100
    },
    "table": {
      "table_name": "cscart_categories",
      "access_type": "eq_ref",
      "possible_keys": ["PRIMARY", "c_status", "p_category_id"],
      "key": "PRIMARY",
      "key_length": "3",
      "used_key_parts": ["category_id"],
      "ref": ["noframes_angrybeaver.cscart_products_categories.category_id"],
      "rows": 1,
      "filtered": 100,
      "attached_condition": "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')"
    }
  }
}