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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '50350263ebb3fd75bfb999af94fb1146cc5aa7fc495f5721e29e7354bed28277' 
  AND token = '78QWmhtdbe03uKWM8MWOw8jwIlVL9teTdIzycmjpi6U=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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