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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a6a76f8d0c052142487042560ce7f7827fd7c9723dd16e7d3f4be353f9ab79e3' 
  AND token = 'xD98fB3eiHehhwKysJLE/cbpV3lS02fHixXeRKUztB4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00035

JSON explain

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