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Thursday, July 27, 2017

SQL Bootcamp



Whatever your focus is when working with data, it helps to know your SQL.  So, enjoying this brush-up from the "Complete SQL Bootcamp" on www.Udemy.com.

In this example using PostgreSQL, it shows how the WHERE clause is used before the HAVING clause.  ...Why?  Well, the HAVING clause was added in SQL to allow selection/filtering by the *grouped* amounts (in this case, aggregated by AVG()), while WHERE filters from the originally-selected records.





Key SQL Note:  Reminder of how different data-types work (in PostgreSQL)






Key SQL Note:  Maybe best diagram of effect of different JOIN-types







Key SQL Note:  Subqueries



















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