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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '50ab1f1b87eb7826306604419ed4da77f03518a13c5998c2f216f1925efa005c' 
  AND token = 'LFNvbX8Nk03TXWtFzD1UuH+AMf8RUy81AcZYptJcOZg=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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