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In the book, "Garcia-Molina H., Ullman J., Widom J., Database Systems: The Complete Book. Pearson Prentice Hall, 2009", Chapter 5, "Algebraic and Logic Query Languages", on top of page 217 of the 2nd edition, there is a box titled "δ is a Special Case of γ", that explains how the duplicate removal operation δ is redundant, since it can be replaced by the use ...


Is there a way to query into the table and grab only those that have unique emails, while ignoring those that share emails? I can think of a couple ways to do this: 1) If I restate this, I might say "Get all of the email addresses that have only 1 entry in the table, and exclude email addresses having more than one entry in the table. Use GROUP ...


I wonder if that works at all, MySQL always had a stupid restriction: You cannot delete from a table and select from the same table in a subquery :-) So create a temporary table first with the result of select min(id) from mytable group by text; And use this in your delete select from mytable where id not in ( select id from mytemptable);

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