How can I do the impossible?
Suppose you're tasked to report on sales figures for the company's sales force. The report has to include the individuals' percentile contribution to the team, region, and company sales in addition to the raw sales numbers. Team percentile contribution to region and total company sales and region percentile contribution to total sales are also needed. You could run multiple queries—one to get the company totals, another to calculate the region totals, a third for the team totals, and finally a detail query by salesperson. Then you would have to perform the matchups of salesperson to team and region and then team to region to calculate the percent contribution for each of those and against the company total sales all in application code. No sweat, right?
Another approach would be to insert correlated subqueries into the projection clause of the query and fetch the percentages that way, but that would be six correlated subqueries across hundreds of salespeople in dozens of teams and regions. This would be the quintessential query from hell!
OK, just to throw a monkey wrench into the mix, C-suite management wants a hard copy report for the Board of Directors, and the sales manager wants an intranet Web page showing the same data but sortable on various columns, and the numbers have to match the hard copy. Oh, and don't forget that the region figures have to go into the annual report for the shareholders, so you'll have to export the data to send to the PR team designing the annual report!
First you think, "Impossible!" Then you think, "I like my job! Or, at least I did before this request came in. So, I have to figure out a way to do this in a single place that can produce identical data for all of these delivery formats. There must be a way to do this in a single SQL statement!" Then you give it a try and rediscover that you cannot mix aggregation data with detail data in a single query. You are back to "Impossible!" Even you can't do the impossible...or can you?
Enter one of the most overused and misused features of SQL '92, derived tables in the FROM clause of a query used as a table entity. The ANSI SQL '92 standard provides the following definition:
A derived table is a table derived directly or indirectly from one or more other tables by the evaluation of a <query expression>. The values of a derived table are derived from the values of the underlying tables when the <query expression> is evaluated.
In effect, the result of any query is a derived table. This agrees with Codd's relational algebra definition that the result of combinations and selections from relations or tuples are themselves relations or tuples.
Enough tech talk, back to brass tacks. When most folk talk about derived tables, they mean using the results of a SELECT query in the FROM clause of a query as if it were a table. Simple example:
SELECT *
FROM ( SELECT col_1, col_2, col_3 FROM sometable) AS d
WHERE ….
Why not just "SELECT * FROM sometable WHERE ...", you ask? So have I. Many times. Too many times! Queries like this "dumb" example are rampant in the real world, but I digress. How can this help with the sales report outlined at the start? You would write queries for each of the aggregation levels and reference them in the FROM clause as derived table expressions. Here's how:
SELECT sm.fname, sm.lname, sm.team_id, sm.region_id, sp.sales,
((sp.sales/tm.sales)*100.00) as team_contribution,
((sp.sales/rs.sales)*100.00) as region_contribution,
((sp.sales/cw.sales)*100.00) as company_contribution,
((tm.sales/rs.sales)*100.00) as team_to_region,_contribution
((tm.sales/cw.sales)*100.00) as team_to_company_contribution,
((rs.sales/cw.sales)*100.00) as region_to_company_contribution,
…
FROM sales_people as sm
JOIN sales_performance as sp
ON sm.sales_id = sp.sales_id
JOIN (
SELECT team_id, sum( sales )
FROM sales_performance
GROUP BY team_id
) AS tm( team_id, sales )
ON sm.team_id = tm.team_id
JOIN (
SELECT region_id, sum( sales )
FROM sales_performance
GROUP BY region_id
) AS rs( region_id, sales )
ON sm.region_id = rs.region_id
JOIN (
SELECT sum( sales )
FROM sales_performance
) AS cw( sales )
ORDER BY sm.lname, sm.fname, sm.region_id, sm.team_id;
To further simplify the various reports and screens that must display these same results, you could create a VIEW based on this query and reference the VIEW in your applications, screens, and reports. VIEW is the common name for the entity type that the SQL standard refers to as a viewed table or a named derived table.
Anyway, this lesson is finished in more than one way. We've defined and described derived tables and used non-trivial ones in the FROM clause of a query in order to achieve "the impossible". All in all, a good day's work. Back to loving your job!
More than ever, there is a demand for IT to deliver innovation. Your IBM i has been an essential part of your business operations for years. However, your organization may struggle to maintain the current system and implement new projects. The thousands of customers we've worked with and surveyed state that expectations regarding the digital footprint and vision of the company are not aligned with the current IT environment.
TRY the one package that solves all your document design and printing challenges on all your platforms. Produce bar code labels, electronic forms, ad hoc reports, and RFID tags – without programming! MarkMagic is the only document design and print solution that combines report writing, WYSIWYG label and forms design, and conditional printing in one integrated product. Make sure your data survives when catastrophe hits. Request your trial now! Request Now.
Forms of ransomware has been around for over 30 years, and with more and more organizations suffering attacks each year, it continues to endure. What has made ransomware such a durable threat and what is the best way to combat it? In order to prevent ransomware, organizations must first understand how it works.
Disaster protection is vital to every business. Yet, it often consists of patched together procedures that are prone to error. From automatic backups to data encryption to media management, Robot automates the routine (yet often complex) tasks of iSeries backup and recovery, saving you time and money and making the process safer and more reliable. Automate your backups with the Robot Backup and Recovery Solution. Key features include:
Business users want new applications now. Market and regulatory pressures require faster application updates and delivery into production. Your IBM i developers may be approaching retirement, and you see no sure way to fill their positions with experienced developers. In addition, you may be caught between maintaining your existing applications and the uncertainty of moving to something new.
IT managers hoping to find new IBM i talent are discovering that the pool of experienced RPG programmers and operators or administrators with intimate knowledge of the operating system and the applications that run on it is small. This begs the question: How will you manage the platform that supports such a big part of your business? This guide offers strategies and software suggestions to help you plan IT staffing and resources and smooth the transition after your AS/400 talent retires. Read on to learn:
LATEST COMMENTS
MC Press Online