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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51a657a0b0aedf26bc41150f25f8b17268c1d5553b035b0fc6bf5775ecae6d42' 
  AND token = 'KiiNjI2gNuN3Ka+JcaGZDcjsnXvuVzAw9lyx2QniUXw=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00033

JSON explain

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