Let us look at an example that is probably realistic for most businesses. We have one datastore for the enterprise that consists of several data servers and a mainframe, collectively called a Data Warehouse or a Distributed Data Processing system. That conglomerate of a datastore receives SQL requests for internal business operations from a business logic server. The business logic server is processing operations as directed by employees using PCs and front-end software on their desks.

Now that you've learned exactly what SQL is? and how to use the standard SELECT functions, it's time to move ahead to other features. In this section, I'll be covering special grouping, logical and mathematical functions. These functions build upon what you've hopefully already learned, and allow you to leverage that to use SQL in your work. While a SELECT statement allows you to look up data in your database, it's far more useful to be able to group and sort the resulting data. Without grouping and sorting, you end up with globs of data, which while they may be useful, are time-consuming to work with.

Your boss has given you a mission. It sounds simple enough - you just need to create a few custom reports on your intranet that connect to your company-wide database. Well, what if suddenly you discover the database is a legacy monstrosity filled with arcane language and structures? What if, heaven forbid, nobody can understand it? How will you keep your job?

SQL is a very utilitarian database environment. Normally, with every database management system comes a new language for construction, querying, reporting, and design. After a while, it becomes rather tiresome, especially with the multiple upgrades to each system, to keep working with different databases. With SQL, however, the language is standardized, thus any SQL-compliant database will adhere to at least some base language structures, affording the development staff greater flexibility in their designs as they can build with relative ease and confidence.

How to use the built-in functions in SQL

How to use AND and OR to join two or more conditions in a WHERE clause.

GROUP BY... was added to SQL because aggregate functions (like SUM) return the aggregate of all column values every time they are called, and without the GROUP BY function it was impossible to find the sum for each individual group of column values.

How to use the DELETE statement to delete rows in a table.

Sometimes we have to select data from two or more tables to make our result complete. We have to perform a join. Tables in a database can be related to each other with keys. A primary key is a column with a unique value for each row. The purpose is to bind data together, across tables, without repeating all of the data in every table. In the "Employees" table below, the "Employee_ID" column is the primary key, meaning that no two rows can have the same Employee_ID. The Employee_ID distinguishes two persons even if they have the same name.

How to use the ORDER BY keywords to return rows in a defined order.