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SQL JOIN

A JOIN combines rows from two tables where a predicate over their columns holds; INNER keeps only matches while LEFT/RIGHT/FULL OUTER preserve unmatched rows padded with NULLs. Logically it is a filter over the cross product — the physical algorithm is the optimizer's choice, not the query author's.

Questions this Concept answers

In the result of an outer join, what do the NULL values inside a preserved row stand for?

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Types of SQL Joins

A SQL JOIN is a query operation, specified in the FROM clause, that combines rows from two or more tables based on a relationship between columns, most commonly a primary key (a column uniquely ident…