A database consists of one or more tables. A table is identified by its name. A table is made up of columns and rows. Columns contain the column name and data type. Rows contain the records or data for the columns.

Each record has a unique identifier or primary key. SQL, which stands for Structured Query Language, is used to communicate with a database. Through SQL one can create and delete tables. Here are some commands:

• CREATE TABLE - creates a new database table
• ALTER TABLE - alters a database table
• DROP TABLE - deletes a database table
• CREATE INDEX - creates an index (search key)
• DROP INDEX - deletes an index

SQL also has syntax to update, insert, and delete records.

• SELECT - get data from a database table
• UPDATE - change data in a database table
• DELETE - remove data from a database table
• INSERT INTO - insert new data in a database table

The SELECT is used to query the database and retrieve selected data that match the specific criteria that you specify:

SELECT "column1" [, "column2", ...]
FROM "tablename"
WHERE "condition"
The conditional clause can include these operators

• = Equal
• > Greater than
• < Less than
• >= Greater than or equal
• <= Less than or equal
• <> Not equal to
• LIKE pattern matching operator

The CREATE TABLE statement is used to create a new table. The format is:
CREATE TABLE "tablename"
("column1" "data type",
"column2" "data type",
"column3" "data type");

• char(size): Fixed length character string.
• varchar(size): Variable-length character string. Max size is specified in parenthesis.
• number(size): Number value with a max number of columns specified in parenthesis
• date: Date value
• number(size,d): A number with a maximum number of digits of "size" and a maximum number of "d" digits to the right of the decimal

Once a table has been created data can be inserted using INSERT INTO command.
INSERT INTO "tablename"
(col1, ... , coln)
VALUES (val1, ... , valn)

To change the data values in a pre existing table, the UPDATE command can be used.
UPDATE "tablename"
SET "colX" = "valX" [, "colY" = "valY", ...]
WHERE "condition"

The DELETE command can be used to remove a record(s) from a table.
DELETE FROM "tablename"
WHERE "condition"

To remove an entire table from the database use the DROP command.
DROP TABLE "tablename"