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 
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') 
WHERE 
  cscart_products_categories.product_id IN (
    13101, 12498, 12496, 12510, 12519, 12516, 
    12530, 12526, 12531, 12509, 12517, 
    12523, 12532, 12525, 12515, 12529, 
    12503, 13100, 12507, 12522, 12508, 
    12506, 12500, 12499, 12513, 12514, 
    13099, 12521, 12527, 12511, 12512, 
    12528, 12520, 12497, 12505, 12502, 
    12504, 10847, 13152, 10846, 10845, 
    10844, 10843, 10842, 10841, 10840, 
    10839, 10838, 10837, 10836, 10835, 
    10834, 10833, 10832, 10831, 10830, 
    10829, 10828, 10827, 12642, 12648, 
    12651, 12645, 12644, 12650, 12649, 
    12643, 12640, 12647, 15800, 12639, 
    12641, 12638, 12637, 12634, 12635, 
    12636, 12654, 12653, 12652
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00102

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": 115,
      "filtered": 100,
      "index_condition": "cscart_products_categories.product_id in (13101,12498,12496,12510,12519,12516,12530,12526,12531,12509,12517,12523,12532,12525,12515,12529,12503,13100,12507,12522,12508,12506,12500,12499,12513,12514,13099,12521,12527,12511,12512,12528,12520,12497,12505,12502,12504,10847,13152,10846,10845,10844,10843,10842,10841,10840,10839,10838,10837,10836,10835,10834,10833,10832,10831,10830,10829,10828,10827,12642,12648,12651,12645,12644,12650,12649,12643,12640,12647,15800,12639,12641,12638,12637,12634,12635,12636,12654,12653,12652)"
    },
    "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')"
    }
  }
}