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15.4 What are the different types of joins? Please explain how they differ and why certain types are better in certain situations. Join是用来联合两个表的，每个表至少 阅读全文
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The Employee table holds all employees including their managers. Every employee has an Id, and there is also a column for the manager Id. Given the Em 阅读全文
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Write a SQL query to find all numbers that appear at least three times consecutively. For example, given the above Logs table, 1 is the only number th 阅读全文
