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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c5821dc09093503b925eee53518fc7c3d81eb3013835ce7600110c5ed8c75272' 
  AND token = 't++UmsETNn5u++R//B4Rn9i/xM1VyK49hW4NPkz+61w=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00036

JSON explain

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