В этом цикле статей автор делится вопросами по SQL, с которыми вы можете столкнуться на собеседовании.
В первой части — базовые темы: первичный и внешний ключ, виды соединений, подзапросы, GROUP BY, CTE и другие часто спрашиваемые концепции.
Во второй — более продвинутые вопросы: подзапросы, индексы, оптимизация запросов, хранимые процедуры, транзакции, представления, функции, денормализация, типы индексов и триггеры.
tags: #статья
BY Java Developer
Bitcoin is built on a distributed digital record called a blockchain. As the name implies, blockchain is a linked body of data, made up of units called blocks that contain information about each and every transaction, including date and time, total value, buyer and seller, and a unique identifying code for each exchange. Entries are strung together in chronological order, creating a digital chain of blocks. “Once a block is added to the blockchain, it becomes accessible to anyone who wishes to view it, acting as a public ledger of cryptocurrency transactions,” says Stacey Harris, consultant for Pelicoin, a network of cryptocurrency ATMs. Blockchain is decentralized, which means it’s not controlled by any one organization. “It’s like a Google Doc that anyone can work on,” says Buchi Okoro, CEO and co-founder of African cryptocurrency exchange Quidax. “Nobody owns it, but anyone who has a link can contribute to it. And as different people update it, your copy also gets updated.”
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