S Q L  

Structured Query Language
CPT 108 · Franklin College · Erich Prisner · 2002-2007

Structured Query Language is the language in which to talk to databases to make them retrieve or update data. It is contained in most relational database system programs, as Access, Oracle, Visual FoxPro, There are several dialects.

SQL commands are written in rows, with key words capitalized, and end with a semicolon.

DML (SQL Data Manipulation Language)

This allows you to extract, change, update, and delete data in tables of a database.

Select

SELECT *
FROM tablename;		 displays a whole table.
SELECT column1, column3
FROM tablename;		 outputs the corresponding columns of the table.
SELECT column1
FROM tablename
WHERE condition; 		outputs the corresponding columns of the table obeying the condition.

The first variant displays certain columns. The second one only certain columns and certain rows. The WHERE-condition could be something like

Try the syntax on this interactive page.

Insert and Update and Delete

INSERT into tablename 
(column1,column3)
VALUES (value1, value3); 		creates a new record with the corresponding values in the columns mentioned. Remember again to enclose all strings into single quotation marks.
UPDATE tablename
SET (column1=value1, column3=value3)
WHERE condition; 		condition could be something like first = 'Erich" and last = 'Prisner'
DELETE from tablename
WHERE condition; 		deletes all records obeying the condition

Others

You can also create tables with SQL, like

CREATE table tablename
(column1 varchar(10), column2 varchar(20), age number(3));

or delete them by DROP table tablename;

DDL (SQL Data Definition Language)

You can create, change, and delete tables, or define or delete keys.