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2

See all of those single letter prefixes followed by a dot and then your column names?...for example the a in a.shop_id. Those are called table aliases and are a way to give nicknames for your tables in a query. But to do that, you must first define them in your FROM and JOIN clauses directly following the table name you want to alias, such as FROM ...


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There is no reliable way to accurately predict the number of pages that will be read. One could estimate the number of blocks by assuming an average number of consecutive rows per block. "100" is a simple estimate that often works. So, unless the rows are big, id in (1,2,3,4,5,6) would probably involve one page. If the ids are scattered all over ...


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If you have the general log enabled at the time of the dump, then there will be a record. But otherwise, no, there isn't a record in the database. You could look at things like shell history, or ssh logins, but its unlikely to yield any specific results.


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First of all, this is not an error, just a "note". If it were an actual error, it would say 'error'. The meaning of the message: An attempt at connecting from this host to one of the two other hosts in the cluster timed out - and the timeout is set to 3 seconds. However, as per the subsequent messages, it then tried connecting again, and thankfully ...


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over is now a keyword -- as of MySQL 8.0. (And there are several other 'new' keywords that will cause syntax errors.) 8.1 (some year) will probably introduce more new keywords. To avoid such in the future, put backtics (`) around each column name and table name.


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