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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '4709021bf482ce2744827bef37297e19003f3a85dfb518c0a7b53ca34312a399' 
  AND token = '21m+TabZbHdpnGTeJLhB7tm8YN8RkhGnDAVp7oyTivg=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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