PHP Dependency Management with Composer
In this article I will introduce you to another great project, Composer. Maybe you’ve experienced the pain of working on a PHP application which uses third-party libraries and then trying to keep them and their dependencies up to date. If so, Composer can soothe your pain.
Composer gets you the libraries you … Read More →
Boxing is the process of converting a value type to the type object or to any interface type implemented by this value type. When the CLR boxes a value type, it wraps the value inside a System.Object and stores it on the managed heap. Unboxing extracts the value type from the object. Boxing is implicit; … Read More →
Heapsort is one of the general sorting algorithms that performs in O(n.log(n)) in the worst-case, just like merge sort and quicksort, but sorts in place – as quicksort. Although quicksort’s worst-case sorting time is O(n2) it’s often considered that it beats other sorting algorithms in practice. Thus in practice quicksort is “faster” than heapsort. In … Read More →
Overview of the WAV Format
The Waveform Audio File Format, also known as WAVE or WAV, is a Microsoft file format standard for storing digital audio data. A WAV file is composed of a set of chunks of different types representing different sections of the audio file. You can envision the format as an HTML page: … Read More →
In today’s world with so many third-party integrations and content-sharing, it’s important to understand and make use of protocols like SCP and SFTP. PHP’s SSH2 extension, a wrapper for libssh2 which implements the SSH2 protocol, provides several functions you can use to securely transfer files.
To begin leveraging these functions, it’s obvious the SSH2 package needs … Read More →
In software engineering, a design patterns are general reusable solutions to a software design problems you find again and again in a real life software development. Patterns are not a finished design that can be transformed directly into your code. They are only formal description or template how to solve specific problem. Patterns are best … Read More →
MySQL implements UNION, but does not directly implement INTERSECTION or DIFFERENCE.
INTERSECTION is just an INNER JOIN on all columns:
drop table if exists a,b;
create table a(i int,j int);
create table b like a;
insert into a values(1,1),(2,2);
insert into b values(1,1),(3,3);
select * from a join b using(i,j);
| i | j |
| 1 | 1 … Read More →
I've had a couple of emails recently about the excellent Stanford Machine Learning and AI online classes, so I thought I'd put up the odd post or two on some of the techniques they cover, and what they might look like in PHP.
The second lecture of the ML class jumps into a simple, but often … Read More →
We’re told that foreign key constraints are the best way to enforce logical referential integrity (RI) in SQL, preventing rows from becoming orphaned. But then we learn that the enforcement of foreign keys incurs a significant performance overhead.1,2
MySQL allows us to set FOREIGN_KEY_CHECKS=0 to disable enforcement of RI when the overhead is too high. But if … Read More →
I have used pivot query for monthly report..
My table is like this:
CREATE TABLE IF NOT EXISTS `attendance` (
`empID` int(11) NOT NULL,
`date` date NOT NULL,
`deptID` int(11) NOT NULL,
`attStatus` varchar(3) NOT NULL,
PRIMARY KEY (`empID`,`date`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1;
For monthly attendance report, I have used this query:
… Read More →
I have a very simple table with three data columns: Date1, Report_#, Name. I would like to pivot it around Date and the various names as the header tab, and have all the report numbers appear below.
So it would LOOK like this:
Report | Date | Name … Read More →
From table tbl( class, member ), you want to cross-tabulate all classes with their members. In SQL terms, you aggregate members over classes. In MySQL:
GROUP BY class;
With that simple query, you're halfway toward cross-tabulation, halfway to implementing a simple CUBE, and halfway to basic entity-attribute-value (EAV) logic. This is easier to see if we have two columns, … Read More →
About the Builder
In the Builder Pattern a director and a builder work together to build an object. The director controls the building and specifies what parts and variations will go into an object. The builder knows how to assemble the object given specification.In this example we have a director, HTMLPageDirector, which is given a builder, … Read More →
OUTER JOIN queries in SQL are susceptible to two very subtle bugs that I’ve observed a number of times in the real world. Daniel and I have been hammering out ways to automatically detect queries that suffer from these bugs, in a relatively new Maatkit tool called mk-query-advisor. It’s part of our series of advisor … Read More →
There is usually more than one way to write a given query, but not all ways are created equal. Some mathematically equivalent queries can have drastically different performance. This article examines one of the motivations for inventing LEFT OUTER join and including it in the SQL standard: improved performance through exclusion joins.
LEFT OUTER join syntax … Read More →
Here’s a way to write join clauses so they are more compact, more readable, and less confusing.
Standard SQL:2003 defines a USING clause that can serve the same function as the ON clause in the familiar JOIN syntax. For example, the following join
select a.col1, b.col2
inner join b on a.col3 = b.col3
May be … Read More →
In this article I’ll show several ways to emulate a FULL OUTER join on a RDBMS that doesn’t support it, as is the case with even the most recent versions of MySQL. This useful query is surprisingly tricky to get right.
A standard SQL FULL OUTER join is like a LEFT or RIGHT join, except that … Read More →
Event delegation is an advanced technique for event-driven programming. The idea: instead of attaching one listener onto each element in a group, attach one listener onto an ancester shared by all the elements in that group. Then, when the listener is triggered, determine whether to act by looking at which element originally received the action.
The … Read More →
Introduction to JSON
Ajax functionality is contained in the global Ajax object. The transport for … Read More →