SELECT 
  redirect_id, 
  src, 
  type, 
  object_id, 
  dest, 
  lang_code 
FROM 
  cscart_seo_redirects 
WHERE 
  src = '/computers/tablets/samsung-galaxy-tab-8-9-wi-fi-only-32gb-metallic-gray'

Query time 0.00018

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}