Used for Retrieving Data, Query Languages

A computer language that's often used on Database Management System (DBMS) and by other artificial language for querying a database or information system, is not a programming language but a query language. A query language is important to a server-side programmer, such as PHP(: Hypertext Preprocessor) developers, because it is a way to get the information that intended for a specific user, into a database. There are classifications of query languages like other computer language, and the popular three for the Web, of them are listed below, base on their popularity:

1. SQL, pronounced not as a word on My Sequel (MySQL) but as just exact as its letter names "S-Q-L", which is short for Structured Query Language and sometimes mistakenly referred as a programming language, instead of a well known class of a database query language for accessing and manipulating relational databases that items are organized in a set of tables, in which item can have relation to another item that's into another table.

   Let Say We've Relational Database Tables:
   - Customers - Orders ID Name 01 Mark 02 Anthony ID No 01 18495 02 82796
   Sample of SQL Queries on Database:
   SELECT Customers . Name AS `Customer` , Orders . No AS `Order No.` FROM Customers INNER JOIN Orders ON Customers . ID = Orders . ID ORDER BY Customers . Name
   SQL Queries' Sample Result:
   Customer Order No. Anthony 82796 Mark 18495

   • MySQL is the most used brand of a free Relational Database Management System (RDBMS) which administering by phpMyAdmin a free web database management for RDBMS. A relational database can be called as a server for storing sensitive data items. Most relational databases are administers by database managements.
     • Generally, a relational database is administering by a database management such phpMyAdmin for MySQL, which can perform various tasks like creating, modifying or deleting a database, table, field or a row, browsing, exporting or operating a table, running SQL query or searching data and more!
2. XPath, the XML Path Language, is a declarative language which is one of the 3 parts of Extensible Stylesheet Language (XSL), used to select nodes from an XML document, and also used by XML Pointer Language (XPointer) to link hyperlinks in XML document to the specific parts of another XML document, and used by XQuery which is built on XPath expressions.

   Let Say We've XML Document:
   <a> <b> <c/> </b> <b> <c/> </b> </a>
   An XPath Example:
   /a/b/c
   That Simple XPath Will:
   Selects "c" elements that are children of "b" elements that are children of the "a" element which is the root or the outermost element of the XML document.

3. XQuery stands for XML Query, it's a query language, just like SQL but instead for a relational database that's in a set of tables, XQuery is for an XML:DBMS a database system which allows data to be stored in XML format, in other words, the XML Database (XML:DB) is in a set of one or more XML documents. An XML:DB have many classifications, and can also use relational which couldn't be called as relational database but “Relational XML:DB” because their data is still in a form of XML.
   • A Native XML Database which can abbreviated as NXD, is a DBMS that entirely built on XML technology, and often embedded XQuery, XML and script editor or Integrated Development Environment (IDE) on their software applications to be as their database managements. Actually, XML:DB in any classification, is rarely used by web coders, and it's very rare to find an online tutoring portal for e-learning XML:DB, unlike PHP (MySQL) Database that can find everywhere.

     "xyz.xml" Document's Sample:
     <x> <y> <z/> </y> <y> <z/> </y> </x>
     XQuery Example:
     doc('xyz.xml')/x/y/z
     Example's Output:
     <z/> <z/>

     • eXist-db is an open source DBMS used to allow the definition, creation, querying, update, and administration of a NXD, that uses XQuery to manipulate its data which is a W3C Recommendation. And because an XML:DB is rarely used, there's no popular choice of XML:DBMS yet.

Keep note that not all classes of query languages are mentioned above! Just the popular three of them that are for web development, and mostly not all the brands of database systems, nor even the database management brands.