Structured Query Language (SQL)                      

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Structured Query Language (SQL), is used by most relational database systems.  Relational databases are databases that have records that correspond to each other.  A typical use of SQL in Microsoft environments is in querying database tables created with Access or Visual Basic.  A typical use of SQL in Unix environments might involve PERL/CGI. 

Keywords:

SELECT - select/retrieve fields from 1 or more tables ORDER BY - criteria for ordering/sorting records
FROM - tables from which to get fields INSERT INTO - insert values into 1 or more tables
WHERE - criteria for rows to be retreived UPDATE - update existing data in specified table(s)
GROUP BY - criteria for grouping DELETE FROM - delete data from specified table
ASC - order ascending DESC - order descending
AND - logical AND OR - logical OR

Example:


SELECT
  Employee ID, FirstName, LastName, SSN, YearBorn, PayRate
   FROM  Employees
       ORDER BY  LastName, FirstName, SSN

---------------------------------------------------------------------------------------------------------------------------------

SELECT
  Employee ID, FirstName, LastName, SSN, PayRate
     FROM Employees
  WHERE  LastName  LIKE  'Germany'
      ORDER BY   SSN   DESC

---------------------------------------------------------------------------------------------------------------------------------

INSERT INTO  Employees(FirstName, LastName)
     VALUES(Charles, Germany)

---------------------------------------------------------------------------------------------------------------------------------

UPDATE  Employees
    SET  SSN = 24698763955
        WHERE  LastName = 'Germany"  AND   FirstName = 'Charles'


Multiple Tables use the dot operator to specify/identify fields from each table:


SELECT
   FirstName, LastName, SSN, PayRate
     FROM Employees, Clients
  WHERE  Employees.LastName Clients.LastName
      ORDER BY   LastName   ASC


We are saying:  From 2 tables, "Employees" and "Clients", select FirstName, LastName, SSN, and PayRate.  Where both
tables have the same last name, order by last name in ascending order.