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 (
    2808, 1523, 2098, 2059, 2065, 1115, 1120, 
    1121, 1124, 1125, 1126, 1132, 1149, 
    1164, 1184, 4470, 2230, 1906
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00234

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "85.61"
    },
    "grouping_operation": {
      "using_filesort": false,
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_products_categories",
            "access_type": "range",
            "possible_keys": [
              "PRIMARY",
              "pt"
            ],
            "key": "pt",
            "used_key_parts": [
              "product_id"
            ],
            "key_length": "3",
            "rows_examined_per_scan": 26,
            "rows_produced_per_join": 26,
            "filtered": "100.00",
            "index_condition": "(`ea201_francemaqu`.`cscart_products_categories`.`product_id` in (2808,1523,2098,2059,2065,1115,1120,1121,1124,1125,1126,1132,1149,1164,1184,4470,2230,1906))",
            "cost_info": {
              "read_cost": "49.21",
              "eval_cost": "5.20",
              "prefix_cost": "54.41",
              "data_read_per_join": "416"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "link_type"
            ]
          }
        },
        {
          "table": {
            "table_name": "cscart_categories",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "c_status",
              "p_category_id"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "category_id"
            ],
            "key_length": "3",
            "ref": [
              "ea201_francemaqu.cscart_products_categories.category_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 1,
            "filtered": "5.00",
            "cost_info": {
              "read_cost": "26.00",
              "eval_cost": "0.26",
              "prefix_cost": "85.61",
              "data_read_per_join": "3K"
            },
            "used_columns": [
              "category_id",
              "usergroup_ids",
              "status",
              "storefront_id"
            ],
            "attached_condition": "((`ea201_francemaqu`.`cscart_categories`.`storefront_id` in (0,1)) and ((`ea201_francemaqu`.`cscart_categories`.`usergroup_ids` = '') or find_in_set(0,`ea201_francemaqu`.`cscart_categories`.`usergroup_ids`) or find_in_set(1,`ea201_francemaqu`.`cscart_categories`.`usergroup_ids`)) and (`ea201_francemaqu`.`cscart_categories`.`status` in ('A','H')))"
          }
        }
      ]
    }
  }
}