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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a3c0308ec858091d0aa06ce71b09d3c5510009d0bb0da8441deb3103aafb9618' 
  AND token = 'hDRa86TzjMg9NJP7jayg0ZkG+p6lTFjMx9GN2ULaiH4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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