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De-duplicating Rows

March 26, 2015 5:19 PM / Leave a comment

dedup them!

dedup these hay-bogarting heffers for me!

Often the need arises to locate and remove duplicated rows, or partially duplicated rows from a table. Queries using the DISTINCT keyword (or it’s synonym UNIQUE) will retrieve and display rows without duplicates. But actually identifying and then removing the unwanted duplicates within a table represents a different level of work, and is also likely to involve greater resource consumption.     Continue…

Set Operators in SQL

February 18, 2015 10:23 AM / 1 Comment on Set Operators in SQL

150px-Edgar_F_Codd

E.F. ‘Ted’ Codd

Relational database design has strong roots within Set Theory, as can be seen in the seminal work of E.F. Codd more than 40 years ago. Most people recall encountering Venn diagrams during their school days, a pictorial excursion into this realm. Codd codified his relational ideals into a series of well-known rules, which represent an extreme case, not taking account of the often necessary pragmatic or performance reasons for selective denormalization. But his principles are still instructive and serve as a starting point for designing business schemas.     Continue…