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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '5473d911afcf9e92e52c10767b44693358d4ae5e5176f56e5f8f8e4c58e3f806' 
  AND token = '51Q5UrBI1E8Wh4pWNHM9IcrZ8mvGWtfm0cLrzzyBeVI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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