Around IT In 256 Seconds
Around IT In 256 Seconds
#34: SQL joins
In relational databases, data is kept in relations, commonly known as tables. Simplifying, when data is normalized, it’s not duplicated. For example, when storing books and authors, you don’t keep an author’s name next to a book record. Instead, you use a so-called foreign key that references the author in another table. Thanks to this level of indirection, books by the same author do not store repeated information. This has many benefits and one, huge drawback. In order to look up a book together with a corresponding author you must somehow correlate these two tables. This is called joining.
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