The Original Hacker's Dictionary

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This article explains some concepts in depth, such as scripting and data types. I shall begin by describing the syntax of a MySQL script, as scripts will be used for all the examples binary option system 4 usa dictionary mathematical systems to this binary option system 4 usa dictionary mathematical systems to.

Instead of issuing each of the SQL statements from a mysql client interactively, it is often more convenience to keep the statements in a script. You could then run the entire script, or copy and paste selected statements to run. Use a programming text editor to create the following script and saved as " testscript. You should use ". You can run the script using mysql client in two ways: To run a script in batch non-interactive mode, start a mysql client and redirect the script as the input, as follows:.

You may provide an absolute or relative path of the filename. You may need to double quote the filename if it contains special characters such as blank strongly binary option system 4 usa dictionary mathematical systems to For example, we invoke the mysql client with user " myuser " in batch mode running the script " testscript. I assume that myuser is authorized to access mysql database. The output contains the column headers binary option system 4 usa dictionary mathematical systems to the rows selected.

The column values are separated by 'tab'. This is to facilitate direct processing by another program. In batch mode, you can also execute statement s directly via -e evaluate option.

An end-of-line comment begins with '-- ' two dashes and a space orwhich lasts till the end of the current line. Comments are ignored by the processing engine but are important to provide explanation and documentation for the script. I strongly encourage you to use binary option system 4 usa dictionary mathematical systems to liberally.

They are recognized by the MySQL engine, but ignored by other database engines. In other words, they will be processed by MySQL but treated as comments by other databases. You could include an optional MySQL version number, e. The statements will be processed by MySQL if the server's version is at least at the specified version, e. MySQL specific codes with version number are often generated when you export a database via mysqldump utility.

Identifiers such as database names, table names and column names must be back-quoted if they contain blanks and special characters; or are reserved word, e. It is a good practice to back-quote all the identifiers in a script to distinguish the names from the reserved words possibly in future MySQL versions.

MySQL keywords are not case-sensitive. For clarity, I often show the keywords in uppercase e. The identifiers such as database names, table names and column names are case sensitive in some platforms; but case insensitive in others e. Hence, it is a good practice to treat the identifiers as case-sensitive in th script. String comparison and sorting depend on the character collation sequence used.

Need to further check on Unixes and Macs. A string literal or string value is enclosed by a pair of single quotes e. Some characters may create ambiguity when placed inside a single-quoted or double-quoted string, e.

Some characters, such as tab, newline, are non-printable, and require a special notation to be included in a sting. An escape followed by any other character listed above is treated as the character, e. The escape sequence is case sensitive, i. String can be single-quoted or double-quoted to give you the flexibility of including quotes in a string without using escape sequence, e. Hex values are written as 0x You can obtain the hex value of a string using function HEX.

Similarly, a bit literal is written as 0b There are various types of variables in MySQL: A user-defined variable begins with a ' ' sign, e. A user-defined variable is connection-specificand is available within a connection. A variable defined in one client session is not visible by another client session.

You may use a user-defined variable to pass a value among SQL statements within the same connection. Like all scripting languages, SQL scripting language is loosely-type. You do not have to explicitly declare the type of a variable, but simply assign a value.

MySQL server maintains system variablesgrouped in two categories: Global variables affect the overall operation of the server. Session variables affect individual client connections. A system variable may have both a global value and a session value. You could use a pattern matching LIKE clause to limit binary option system 4 usa dictionary mathematical systems to outputs. Local Variables within a Stored Program: You could define local variables for stored programs such as function and procedure.

The scope of a local variable is within the program. Local variable will be discussed later. As a programmer, understanding the data types is curial in understanding the working of the underlying database system.

The field-width affects only the display, and not the number stored. Choosing the right integer type is important for optimizing storage usage and computational efficiency. Example Testing the Integer Data Types: Example Testing the Floating-point Data Type: Strings are made up of a sequence of characters. Before presenting the various string data types, it is important to understand the so-called character set and collating sequence or collation. A character set also called charsetcharacter encodingcharacter mapcode page defines a set of character and maps each character to a unique numeric code.

A collating sequence or collation refers to the orders in which individual characters should be ranked in comparing or sorting the strings. In other words, a collation is a set of rules for ranking characters in a character set. A string may contain uppercase and lowercase characters, digits and symbols. As an example, suppose we wish to sort three strings: Ranking strings according to their underlying code numbers is known as binary collation.

Binary collation does not agree with the so-called dictionary orderwhere the same uppercase and lowercase letters have the same rank. There are many other collating sequences available. Some case-insensitive ci dictionary-order collating sequences have the same rank for the same uppercase and lowercase letter, i.

Some case-sensitive cs dictionary-order collating sequences put the uppercase letter before its lowercase counterpart, i. Typically, space is binary option system 4 usa dictionary mathematical systems to before digits '0' to '9'followed by the alphabets. Collating sequence is also language dependent, as different languages use different sets of characters, e.

It becomes more complicated if more than one languages are used, e. You can list the available collations for latin1as follows:. I recommend that you use utf8 charset for applications that require internationalization i18n support because utf8 supports all the languages in this world.

Other collations for utf8 includes:. You may want to try out some of these collations by ranking space, numbers, uppercase and lowercase letters, and some typical strings. They could be set at 4 levels: The default charset is latin1. Example Testing Character Sets and Collations: You can list them as follows:. In MySQL, columns, tables, databases may use different character sets. However, the meta-data such as column names and attributes must be stored in online trading account uae same character set, and include all languages.

A client connects to the server via a so-called connection object. The client sends the SQL statements over the connection to the server. The server returns the results via the connection to the client. Server maintains a connection for each client, and maintains connection-related character set and collation system variables for each client connection.

When a client e. A string literal has on optional charset introducer and collate clause. The introducer tells the parser that the string that is followed uses a certain character set.

String introducer merely interpret s the string literal and does not change its value; whereas CONVERT returns a new value of the specified type. If you want to display a text file encoded in a particular character set e. To set the codepage in CMD, issue command " chcp color-page-number ", e. There are a number of character encoding schemes for Chinese characters, binary option system 4 usa dictionary mathematical systems to.

Unicode has two frequently-used encoding schemes:

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It is often derided as being a toy, but beneath its layer of deceptive simplicity, powerful language features await.

JavaScript is now used by an incredible number of high-profile applications, showing that deeper knowledge of this technology is an important skill for any web or mobile developer. It's useful to start with an overview of the language's history. JavaScript was created in by Brendan Eich while he was an engineer at Netscape.

JavaScript was first released with Netscape 2 early in It was originally going to be called LiveScript, but it was renamed in an ill-fated marketing decision that attempted to capitalize on the popularity of Sun Microsystem's Java language — despite the two having very little in common. This has been a source of confusion ever since. It was a mostly-compatible JavaScript work-alike. The standard received a significant update as ECMAScript edition 3 in , and it has stayed pretty much stable ever since.

The fourth edition was abandoned, due to political differences concerning language complexity. Many parts of the fourth edition formed the basis for ECMAScript edition 5, published in December of , and for the 6th major edition of the standard, published in June of Unlike most programming languages, the JavaScript language has no concept of input or output.

It is designed to run as a scripting language in a host environment, and it is up to the host environment to provide mechanisms for communicating with the outside world. The most common host environment is the browser, but JavaScript interpreters can also be found in a huge list of other places, including Adobe Acrobat, Adobe Photoshop, SVG images, Yahoo's Widget engine, server-side environments such as Node.

JavaScript is a multi-paradigm, dynamic language with types and operators, standard built-in objects, and methods. Its syntax is based on the Java and C languages — many structures from those languages apply to JavaScript as well. JavaScript supports object-oriented programming with object prototypes, instead of classes see more about prototypical inheritance and ES classes.

JavaScript also supports functional programming — functions are objects, giving functions the capacity to hold executable code and be passed around like any other object.

Let's start off by looking at the building blocks of any language: JavaScript programs manipulate values, and those values all belong to a type.

And Array , which is a special kind of object. And Date and RegExp , which are objects that you get for free.

And to be technically accurate, functions are just a special type of object. So the type diagram looks more like this:. And there are some built-in Error types as well. Things are a lot easier if we stick with the first diagram, however, so we'll discuss the types listed there for now.

This has some interesting consequences. There's no such thing as an integer in JavaScript, so you have to be a little careful with your arithmetic if you're used to math in C or Java. In practice, integer values are treated as bit ints, and some implementations even store it that way until they are asked to perform an instruction that's valid on a Number but not on a bit integer.

This can be important for bit-wise operations. The standard arithmetic operators are supported, including addition, subtraction, modulus or remainder arithmetic, and so forth. There's also a built-in object that we forgot to mention earlier called Math that provides advanced mathematical functions and constants:.

You can convert a string to an integer using the built-in parseInt function. This takes the base for the conversion as an optional second argument, which you should always provide:. In older browsers, strings beginning with a "0" are assumed to be in octal radix 8 , but this hasn't been the case since or so.

Unless you're certain of your string format, you can get surprising results on those older browsers:. Here, we see the parseInt function treat the first string as octal due to the leading 0, and the second string as hexadecimal due to the leading "0x".

The hexadecimal notation is still in place ; only octal has been removed. Similarly, you can parse floating point numbers using the built-in parseFloat function. Unlike its parseInt cousin, parseFloat always uses base A special value called NaN short for "Not a Number" is returned if the string is non-numeric:. You can test for NaN using the built-in isNaN function:. JavaScript also has the special values Infinity and -Infinity:.

Strings in JavaScript are sequences of Unicode characters. This should be welcome news to anyone who has had to deal with internationalization. More accurately, they are sequences of UTF code units; each code unit is represented by a bit number. Each Unicode character is represented by either 1 or 2 code units. If you want to represent a single character, you just use a string consisting of that single character. To find the length of a string in code units , access its length property:.

There's our first brush with JavaScript objects! Did we mention that you can use strings like objects too? They have methods as well that allow you to manipulate the string and access information about the string:. JavaScript distinguishes between null , which is a value that indicates a deliberate non-value and is only accessible through the null keyword , and undefined , which is a value of type undefined that indicates an uninitialized value — that is, a value hasn't even been assigned yet.

We'll talk about variables later, but in JavaScript it is possible to declare a variable without assigning a value to it. If you do this, the variable's type is undefined. JavaScript has a boolean type, with possible values true and false both of which are keywords. Any value can be converted to a boolean according to the following rules:. However, this is rarely necessary, as JavaScript will silently perform this conversion when it expects a boolean, such as in an if statement see below.

For this reason, we sometimes speak simply of "true values" and "false values," meaning values that become true and false , respectively, when converted to booleans.

Alternatively, such values can be called "truthy" and "falsy", respectively. New variables in JavaScript are declared using one of three keywords: The declared variable is available from the block it is enclosed in. The following is an example of scope with a variable declared with let:. The variable is available from the block it is declared in. It does not have the restrictions that the other two keywords have. This is because it was traditionally the only way to declare a variable in JavaScript.

A variable declared with the var keyword is available from the function it is declared in. An important difference between JavaScript and other languages like Java is that in JavaScript, blocks do not have scope; only functions have a scope.

So if a variable is defined using var in a compound statement for example inside an if control structure , it will be visible to the entire function. However, starting with ECMAScript , let and const declarations allow you to create block-scoped variables. These can be used as a prefix or postfix operators.

If you add a string to a number or other value everything is converted in to a string first. This might catch you up:. These work for both strings and numbers. Equality is a little less straightforward. The double-equals operator performs type coercion if you give it different types, with sometimes interesting results:. JavaScript also has bitwise operations. If you want to use them, they're there. JavaScript has a similar set of control structures to other languages in the C family.

Conditional statements are supported by if and else ; you can chain them together if you like:. JavaScript has while loops and do-while loops. The first is good for basic looping; the second for loops where you wish to ensure that the body of the loop is executed at least once:.

JavaScript's for loop is the same as that in C and Java: JavaScript also contains two other prominent for loops: This is useful for checking for null objects before accessing their attributes:. If you don't add a break statement, execution will "fall through" to the next level.

This is very rarely what you want — in fact it's worth specifically labeling deliberate fallthrough with a comment if you really meant it to aid debugging:. The default clause is optional. JavaScript objects can be thought of as simple collections of name-value pairs. As such, they are similar to:. The fact that this data structure is so widely used is a testament to its versatility. Since everything bar core types in JavaScript is an object, any JavaScript program naturally involves a great deal of hash table lookups.

It's a good thing they're so fast! The "name" part is a JavaScript string, while the value can be any JavaScript value — including more objects. This allows you to build data structures of arbitrary complexity. These are semantically equivalent; the second is called object literal syntax and is more convenient. This syntax is also the core of JSON format and should be preferred at all times. These are also semantically equivalent. The second method has the advantage that the name of the property is provided as a string, which means it can be calculated at run-time.