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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51ae369dc6760a464be7c034368fc52e7dd30f4be9cb136ea1d1012294d8cde1' 
  AND token = '4KvoOQKjnkKW/Zmn3rVCVtm7alzQMKkUjp+QNyUSHTE=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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