In this post, we continue discussing the functionality of the WHERE clause. We started with the basics of the logic using things like AND, OR, and LIKE or '='. Now, we'll expand into some other areas.
Functions in the WHERE Clause
SQL Server provides you with all sorts of functions that can be used to manipulate strings, modify dates or times or perform arcane mathematical equations. The problem with these is that if you do them on columns in tables it can lead to performance issues. The trick then, is to not perform functions on the columns in the tables. We'll cover this in more detail when we get to indexing, variables, and parameters. Just don't get into the habit of putting functions on the columns in your tables in the WHERE clause.
Database Fundamentals #22: Using the Join Operator, CROSS JOIN
While the CROSS JOIN is not used much, and, depending on the size of your data it can be dangerous, there are some uses for it. For example, you may want to write a query that will summarize all the sales for the companies and people in your system. You can do this using what is called an aggregate operation or a GROUP BY:
SELECT c.CompanyName,
p.LastName,
SUM(ft.TransactionAmount) AS 'TransactionTotals'
FROM Management.Company AS c
JOIN Finance.FinancialTransaction AS ft
ON c.CompanyID = ft.CompanyID
JOIN Personnel.Person AS p
ON p.PersonID = ft.PersonID
GROUP BY c.CompanyName, p.LastName;You might also like: Overview of SQL Joins in SQL Server
This will add all the values up in the SUM operation for each company and each person that has values so that your data will look like this:
Database Fundamentals #21: Using the JOIN Operator, OUTER JOIN
The OUTER JOIN returns one complete set of data and then the matching values from the other set. The syntax is basically the same as INNER JOIN but you have to include whether or not you're dealing with a RIGHT or a LEFT JOIN. The OUTER word, just like the INNER key word, is not required.
OUTER JOIN
Imagine a situation where you have a list of people. Some of those people have financial transactions, but some do not. If you want a query that lists all people in the system, including those with financial transactions, the query might look like this: