Mysql count 可以以不同的方式使用。以下是我们可以使用的3种方法。
func BuyButton(sender:UIButton) {
print("clicked cell is at row \(sender.tag)")
let indexPath = NSIndexPath(row: sender.tag, section: 0)
let currentCell = tableView.cellForRow(at: indexPath as IndexPath) as! CustomCell
let Storyboard = UIStoryboard(name: "Main", bundle: nil)
let PaymentController = Storyboard.instantiateViewController(withIdentifier: "PaymentViewController") as! PaymentViewController
print(currentCell.Test.text!) //prints fine here
PaymentController.RecordTitle = currentCell.Test.text!
self.presentViewController(PaymentController, animated: false, completion: nil)
}
SELECT COUNT(table_1.id) FROM <data set with many joints>;
SELECT COUNT(*) FROM (SELECT table_1.id FROM <data set with many joints>);
上述查询的效果是否有任何差异？有人可以解释考虑并发吗？