Introduction to SQL

Introduction to SQL : Introduction to SQL is explained in the easy way. SQL is a standard language for accessing and manipulating databases.

What is SQL?

  • SQL stands for Structured Query Language
  • SQL lets you access and manipulate databases
  • SQL is an ANSI (American National Standards Institute) standard

What Can SQL do?

  • SQL can execute queries against a database
  • SQL can retrieve data from a database
  • SQL can insert records in a database
  • SQL can update records in a database
  • SQL can delete records from a database
  • SQL can create new databases
  • SQL can create new tables in a database
  • SQL can create stored procedures in a database
  • SQL can create views in a database
  • SQL can set permissions on tables, procedures, and views

SQL is a Standard – BUT….

  • Although SQL is an ANSI (American National Standards Institute) standard, there are different versions of the SQL language.
  • However, to be compliant with the ANSI standard, they all support at least the major commands (such as SELECT, UPDATE, DELETE, INSERT, WHERE) in a similar manner.

Note:

Most of the SQL database programs also have their own proprietary extensions in addition to the SQL standard!

Using SQL in Your Web Site

To build a web site that shows data from a database, you will need:

  • An RDBMS database program (i.e. MS Access, SQL Server, MySQL)
  • To use a server-side scripting language, like PHP or ASP
  • To use SQL to get the data you want
  • To use HTML / CSS to style the page

RDBMS

  • RDBMS stands for Relational Database Management System.
  • RDBMS is the basis for SQL, and for all modern database systems such as MS SQL Server, IBM DB2, Oracle, MySQL, and Microsoft Access.
  • The data in RDBMS is stored in database objects called tables. A table is a collection of related data entries and it consists of columns and rows.
  • Look at the “Customers” table:

Example

SELECT * FROM Customers;

 

Output

Number of Records: 10

CustomerID CustomerName ContactName Address City PostalCode Country
1 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico
4 Around the Horn Thomas Hardy 120 Hanover Sq. London WA1 1DP UK
5 Berglunds snabbköp Christina Berglund Berguvsvägen 8 Luleå S-958 22 Sweden
6 Blauer See Delikatessen Hanna Moos Forsterstr. 57 Mannheim 68306 Germany
7 Blondel père et fils Frédérique Citeaux 24, place Kléber Strasbourg 67000 France
8 Bólido Comidas preparadas Martín Sommer C/ Araquil, 67 Madrid 28023 Spain
9 Bon app’ Laurence Lebihans 12, rue des Bouchers Marseille 13008 France
10 Bottom-Dollar Marketse Elizabeth Lincoln 23 Tsawassen Blvd. Tsawassen T2F 8M4 Canada

 

  • Every table is broken up into smaller entities called fields. The fields in the Customers table consist of CustomerID, CustomerName, ContactName, Address, City, PostalCode and Country.
  • A field is a column in a table that is designed to maintain specific information about every record in the table.
  • A record, also called a row, is each individual entry that exists in a table.
  • For example, there are 91 records in the above Customers table.
  • A record is a horizontal entity in a table.
  • A column is a vertical entity in a table that contains all information associated with a specific field in a table.

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