Как понять логику EXISTS в SQL запросах
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Как следует из названия, данная статья для тех, у кого есть сложности с пониманием SQL запросов, в составе которых, используется EXISTS, т.к., исходя из опыта, его использование частенько вызывает вопросы у начинающих, а иногда даже у продолжающих.
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Bitcoin is a decentralized digital currency that you can buy, sell and exchange directly, without an intermediary like a bank. Bitcoin’s creator, Satoshi Nakamoto, originally described the need for “an electronic payment system based on cryptographic proof instead of trust.” Each and every Bitcoin transaction that’s ever been made exists on a public ledger accessible to everyone, making transactions hard to reverse and difficult to fake. That’s by design: Core to their decentralized nature, Bitcoins aren’t backed by the government or any issuing institution, and there’s nothing to guarantee their value besides the proof baked in the heart of the system. “The reason why it’s worth money is simply because we, as people, decided it has value—same as gold,” says Anton Mozgovoy, co-founder & CEO of digital financial service company Holyheld.
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