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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'df03986fb9d7f38c908b2cb6e062deeb2abb6dfb31becd123ebe2555a7e9afef' 
  AND token = '/N8tdlI8uYbFcS9ZduqvmfNCRmwvAQb7OBwoN9e9/Rc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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