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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '6256c68bc414241015136eaa3ad1d681a46f740e582510ad5759c752ad078af9' 
  AND token = '6SWW1sPVFTY8RRSt19tsefiZfg6fgXOUyCPfDvjacOQ=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00055

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE noticed after reading const tables"
    }
  }
}