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
Durov said on his Telegram channel today that the two and a half year blockchain and crypto project has been put to sleep. Ironically, after leaving Russia because the government wanted his encryption keys to his social media firm, Durov’s cryptocurrency idea lost steam because of a U.S. court. “The technology we created allowed for an open, free, decentralized exchange of value and ideas. TON had the potential to revolutionize how people store and transfer funds and information,” he wrote on his channel. “Unfortunately, a U.S. court stopped TON from happening.”
In recent times, Telegram has gained a lot of popularity because of the controversy over WhatsApp’s new privacy policy. In January 2021, Telegram was the most downloaded app worldwide and crossed 500 million monthly active users. And with so many active users on the app, people might get messages in bulk from a group or a channel that can be a little irritating. So to get rid of the same, you can mute groups, chats, and channels on Telegram just like WhatsApp. You can mute notifications for one hour, eight hours, or two days, or you can disable notifications forever.
SQL для тестировщика from id