SELECT 
  products_pattern_id 
FROM 
  cscart_ecl_meta_tags_categories_patterns 
WHERE 
  category_id = 324

Query time 0.00021

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE noticed after reading const tables"
    }
  }
}