Задача про бинарное дерево
#почитать
Пару слов о необходимом арсенале. Для решения задачи, понадобится следующее:
▫️Изучить, либо освежить, как используются, в SQL, условные конструкции CASE WHEN THEN;
▫️Повторить использование IN в связке с вложенным запросом, а именно, перед ним.
▫️Вспомнить, что делает оператор DISTINCT;
Ну и не забывать, что когда проверяем значение на NULL, то пишем не '=', '<>', '!=' а IS NULL / IS NOT NULL.
BY SQL для тестировщика
To pay the bills, Mr. Durov is issuing investors $1 billion to $1.5 billion of company debt, with the promise of discounted equity if the company eventually goes public, the people briefed on the plans said. He has also announced plans to start selling ads in public Telegram channels as soon as later this year, as well as offering other premium services for businesses and users.
Secure video calling is in high demand. As an alternative to Zoom, many people are using end-to-end encrypted apps such as WhatsApp, FaceTime or Signal to speak to friends and family face-to-face since coronavirus lockdowns started to take place across the world. There’s another option—secure communications app Telegram just added video calling to its feature set, available on both iOS and Android. The new feature is also super secure—like Signal and WhatsApp and unlike Zoom (yet), video calls will be end-to-end encrypted.
SQL для тестировщика from nl