SELECT 
  redirect_id, 
  src, 
  type, 
  object_id, 
  dest, 
  lang_code 
FROM 
  cscart_seo_redirects 
WHERE 
  src = '/retour-gratuit'

Query time 0.00013

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_seo_redirects",
      "access_type": "ref",
      "possible_keys": ["src"],
      "key": "src",
      "key_length": "767",
      "used_key_parts": ["src"],
      "ref": ["const"],
      "rows": 1,
      "filtered": 100,
      "index_condition": "cscart_seo_redirects.src = '/retour-gratuit'"
    }
  }
}