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 (
    12570, 12578, 12568, 12547, 12569, 12584, 
    12592, 12575, 12574, 12550, 12544, 
    12564, 12577, 12579, 12555, 12560, 
    12556, 12561, 12572, 12583, 12591, 
    12582, 12590, 12571, 12632, 12559, 
    12631, 10596, 10597, 10598, 10599, 
    10600, 10521, 10520, 10519, 10518, 
    10517, 10516, 10515, 10514, 10513, 
    10512, 10511, 10510, 10509, 10508, 
    10507, 10506, 10505, 10504, 10503, 
    10502, 10501, 10500, 10499, 10498, 
    10497, 9839, 12702, 9841, 9848, 9840, 
    9844, 9843
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00129

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": 91,
      "filtered": 100,
      "index_condition": "cscart_products_categories.product_id in (12570,12578,12568,12547,12569,12584,12592,12575,12574,12550,12544,12564,12577,12579,12555,12560,12556,12561,12572,12583,12591,12582,12590,12571,12632,12559,12631,10596,10597,10598,10599,10600,10521,10520,10519,10518,10517,10516,10515,10514,10513,10512,10511,10510,10509,10508,10507,10506,10505,10504,10503,10502,10501,10500,10499,10498,10497,9839,12702,9841,9848,9840,9844,9843)"
    },
    "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')"
    }
  }
}