Skip to main content

The INNER JOIN Keywords


The form of inner join syntax just discussed uses the comma operator in the FROM clause to name the
joined tables. Another inner join syntax uses the INNER JOIN keywords. With this syntax, those
keywords replace the comma operator between table names in the FROM clause. Also, with INNER JOIN,the conditions that indicate how to perform record matching for the tables move from the WHERE clause to become part of the FROM clause.
There are two syntaxes for specifying matching conditions with INNER JOIN queries:

• Add ON and an expression that states the required relationship between tables. Suppose that a join
performs a country code match between the CountryLanguage and Country tables. The join
would be written as follows:

SELECT Country.Name, CountryLanguage.Language FROM CountryLanguage INNER JOIN Country
ON CountryLanguage.CountryCode = Country.Code;

• If the name of the joined column is the same in both tables, add USING() rather than ON after the
table names, and list the name within the parentheses. For example, if the country code column
happened to be named CountryCode in both tables, the query could be written like this:

SELECT Country.Name FROM City INNER JOIN CountryLanguage USING (CountryLanguage.CountryCode)
WHERE CountryLanguage.Language='Turkish';

If tables using more than one pair of like-named columns are being joined, list the column names
within the parentheses of the USING() clause separated by commas.

The ON Clause

Similar to WHERE, the ON clause in a join specifies how to match records in the joined tables, and
eliminates non-corresponding combinations of rows from the output. The ON clause also can include
additional conditions to further restrict the output and answer more specific questions. Here are some
examples:

• In which countries is the Swedish language spoken? To answer this, include a condition that
identifies the language desired:

mysql> SELECT Country.Name, CountryLanguage.Language
-> FROM CountryLanguage INNER JOIN Country
-> ON CountryLanguage.CountryCode = Country.Code
-> AND Language = 'Swedish';


+---------+----------+
| Name | Language |
+---------+----------+
| Norway | Swedish |
| Sweden | Swedish |
| Finland | Swedish |
| Denmark | Swedish |
+---------+----------+
Labels:

Comments

Post a Comment

Popular posts from this blog

PHP INTRODUCTION

                     PHP  (recursive acronym for  PHP: Hypertext Preprocessor ) is a widely-used open source general-purpose scripting language that is especially suited for web development and can be embedded into HTML. PHP stands for  P HP:  H ypertext  P reprocessor PHP is a server-side scripting language, like ASP PHP scripts are executed on the server PHP supports many databases (MySQL, Informix, Oracle, Sybase, Solid, PostgreSQL, Generic ODBC, etc.) PHP is an open source software PHP is free to download and use Why PHP? PHP runs on different platforms (Windows, Linux, Unix, etc.) PHP is compatible with almost all servers used today (Apache, IIS, etc.) PHP is FREE to download from the official PHP resource:  www.php.net PHP is easy to learn and runs efficiently on the server side What can PHP do? Anything. PHP is mainly focused on server-side scripting, so you can...
6 comments
Read more

Data Encryption

Data encryption is the process of scrambling stored or transmitted information so that it is unintelligible until it is unscrambled by the intended recipient. The intended recipient can then decode (or decrypt) the information. PHP offers multiple means to make this happen. However, none of these solutions are very effective without the applications running on secure servers and connections. The following are a list of the more common encryption functions in PHP: • md5() - MD5 is a third-party hash algorithm that PHP can use to create a digital fingerprint of a piece of data. It is next to impossible to (efficiently) recover the original text when a piece of data has been encrypted with the md5 hash algorithm. It is also vastly unlikely that any different text string will create an identical hash - a 'hash collision'. These properties make hashes ideally suited for storing an application's passwords because although an attacker may compromise a part of the system...
2 comments
Read more

Delimiting PHP Code

                           PHP was originally designed to be used in conjunction with a web server, and in the case of the LAMP architecture, the Apache Web Server.  PHP applications are designed embedding PHP scripts within a web page along with its HTML.  Unlike standard HTML pages which are sent directly from the web server to the end user, PHP files are first interpreted by the PHP application which then converts the PHP script into another form for display.  This process eliminates the end user from being able to see the original PHP script that was embedded in the HTML and provides  true interaction in HTML files.  This process is similar to proprietary applications such as ASP and Coldfusion; however, PHP is Open Source and cross- platform. PHP Tags             PHP scripts are distinguished from the HTML scripts by using delimiting characters ...
1 comment
Read more