Last week's article shed some light on the Outer Joins in SELECT queries. It's a JOIN type that returns both matched and unmatched rows from related tables. Unfortunately, it is not supported by all database (DB) vendors, including MySQL. But that's OK, because Outer Joins can be emulated by combining three other JOIN types, namely LEFT, INNER, and RIGHT joins. In this article, we'll learn more about LEFT and RIGHT joins and how, when combined with an INNER JOIN, they create an OUTER JOIN.
The Outer Join is the least understood of all the SQL Join types. Perhaps it's because Outer Joins are required somewhat less often than other join types. In any case, there is nothing inherently strange about Outer Joins. As we'll see in this blog article, a few examples of the Outer Join in action should be enough to clarify any misapprehensions and/or confusion you may have about them.
This blog will first describe the syntax and purpose of the Outer Join statement, which will then be followed by some illustrative examples.
In the realm of Information Technology, or IT as it's more commonly known, an enum is a special data type that encapsulates a set of predefined constants. As such, the variable may only hold one of the values that have been predefined for it. Common examples include compass directions of NORTH, SOUTH, EAST, and WEST or the days of the week.
One of the complicating factors when storing enums in a database table is that their values may be numeric or alphabetic (i.e. strings). Moreover, you'll want to prevent users from adding any values to the table that are not part of the permissible enum set. We'll be addressing both of these issues in today's blog.
Strings as Primary Keys
In this third and final installment of this series on choosing a Primary Key for relational databases we'll be examining some of the reasons for employing string data as a Primary Key (PK). Recall that, in Part 1, we covered Natural and Surrogate Primary Keys and considered why one might choose one over the other. Part 2 explored String and Numeric data types as Primary Keys in an effort to ascertain whether one is preferable to the other. Now it's time to set the record straight and conclude whether or not string - or alphabetic - data can make a suitable PK.
String vs. Numeric Data Types as Primary Keys
Welcome back to this series on choosing a Primary Key for relational databases. In Part 1, we covered Natural and Surrogate Primary Keys and considered why one might choose one over the other. Today's instalment will explore String and Numeric data types as Primary Keys in an effort to ascertain whether one is preferable to the other.
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