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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51bc641788774762653ed842f0090c13f865c3993d6a2a864d9c4132bb10f5e0' 
  AND token = 'Avg52j7ccrSWqkVEABCxYg+0KP5zmdeQbCnF273b+tM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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