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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '50b11f68f86852a5e29eb1cf4e2f09afc096b29c1d84917bf50c0944b2dd9c91' 
  AND token = 'ST0u1ZsTdY4tB9Y4XMyom+cB7GnWrNUptrKrFD18kq8=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00036

JSON explain

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