SELECT 
  * 
FROM 
  cscart_ap_categories 
where 
  category_id = 4

Query time 0.00093

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_ap_categories",
      "access_type": "ALL",
      "rows": 7,
      "filtered": 100,
      "attached_condition": "(`_testcscart`.`cscart_ap_categories`.`category_id` = 4)"
    }
  }
}