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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b6f3c28ad963cf8fe576f2fb7ba5bd85a79bcbbe406638c2f01e841f356eeb5c' 
  AND token = 'JCX+v99XkDUSqo9eWMb217nYp2phrlChv9SWKAfuJNQ=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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