Introduction to SQL

SQL may frequently pronounced �sequel� but the alternate pronunciation �S.Q.L.� is also used. As the name implies, SQL is a computer language that you use to interact with a database. In fact, SQL works with a specific type of database, called a relational database.

SQL is more than a query tool, although that was its original purpose, and retrieving data is still one of its most important functions. SQL is used to control all of the functions of DBMS which provides for its users, including:

Data Definition Language. In DDL user define the structure and organization of the stored data and relationships among the stored data items.

Data Retrieval Language. An application program to retrieve stored data from the database and use it.

Data Manipulation Language. DML allows a user or an application program to update the database by adding new data, removing old data, and modifying previously stored data.

Data Control Language. DCL can be used to restrict a user�s ability to retrieve, add, and modify data, protecting stored data against unauthorized access.

Data sharing. Is used to coordinate data sharing by concurrent users, ensuring that they do not interfere with one another.

Data intigrity.It defines integrity constraints in the database, protecting it from corruption due to inconsistent updates or system failures.

SQL Queries

Query is a loose term that refers to a widely available set of SQL commands called clauses. Each clause or command performs some sort of function against the database. For instance, the create clause creates tables in databse and the select clause selects rows that have been inserted into your tables.

Construction of Query begins with one of the following clauses:

Add
Drop
Create
Insert
Select
Update
Replace
Delete

SQL Query Syntax

The syntax of a query is loose, meaning you are free to place line breaks and spacing where you please without injuring the code.Few instances require parentheses, including the insert statement listed below. Parentheses will also be covered during our Functions lesson. Be sure to end all query statements with a semicolon (;).

SQL Code:

SELECT * FROM table_name;

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