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 (
    19938, 19939, 19940, 19941, 19943, 19600, 
    19601, 18570, 14106, 14070, 14045, 
    14051, 14044, 14097, 14093, 14105, 
    14125, 18488, 18489, 18600, 18603
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00051

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.058361468,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_products_categories",
          "access_type": "range",
          "possible_keys": ["PRIMARY", "pt"],
          "key": "pt",
          "key_length": "3",
          "used_key_parts": ["product_id"],
          "loops": 1,
          "rows": 21,
          "cost": 0.022871025,
          "filtered": 100,
          "attached_condition": "cscart_products_categories.product_id in (19938,19939,19940,19941,19943,19600,19601,18570,14106,14070,14045,14051,14044,14097,14093,14105,14125,18488,18489,18600,18603)",
          "using_index": true
        }
      },
      {
        "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": ["u508912950_dev_2025.cscart_products_categories.category_id"],
          "loops": 21,
          "rows": 1,
          "cost": 0.02206004,
          "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')"
        }
      }
    ]
  }
}