Perhaps the most powerful SQL feature is the JOIN operation. It is the envy of all non-relational databases, because the concept is so simple, yet so universally applicable, when you want to "combine" two data sets. Put simply, when joining two tables, you're combining every row from one table with every row from another table, … Continue reading A Probably Incomplete, Comprehensive Guide to the Many Different Ways to JOIN Tables in SQL
Tag: INNER JOIN
SQL JOIN or EXISTS? Chances Are, You’re Doing it Wrong
A lot of developers get the distinction between JOIN and SEMI-JOIN wrong. Let me explain... What are JOIN and SEMI-JOIN A little bit of relational algebra first. What is an (INNER) JOIN? An JOIN is nothing but a filtered cartesian product. And what is a cartesian product? Wikipedia explains this very nicely: for sets A … Continue reading SQL JOIN or EXISTS? Chances Are, You’re Doing it Wrong