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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '921009a426b247c6a39fb8a008fc1df0b56dee90247d0d984aec3bb6f438bad9' 
  AND token = 'USZyyUSslG87AEW1nswSNYLTfjIgIEElKy3HCJmJRFk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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