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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a6c8d1b9868a1deb458e8d5a3afcf0511ddcaf7d56d4e4444b930c394cdd0155' 
  AND token = '9HBBTUBjPzXWFXQySBSrjbZjhlZ8d+ZjFVj/Or7wVXw=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00039

JSON explain

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