SELECT 
  category_id 
FROM 
  netting_categories 
WHERE 
  category_type = 'D'

Query time 0.00036

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "netting_categories",
          "access_type": "ALL",
          "rows": 180,
          "filtered": 100,
          "attached_condition": "netting_categories.category_type = 'D'"
        }
      }
    ]
  }
}