SQL is a language used to store, manipulate, and retrieve data in a relational database. SQL was the first commercial language for relational databases and is now used by almost all relational database management systems. SQL functions are divided into two categories: data definition language (DDL) and data manipulation language (DML). DDL is used to define the database structure and includes commands like CREATE, ALTER, TRUNCATE, and DROP to create, modify, delete data from, and drop tables. The ALTER command can be used to add or drop columns from an existing table.

1. STRUCTURED
QUERY
LANGUAGE
Marilou Jamis

2. SQL
• SQL is structured query language, which is a computer
language for storing, manipulating and retrieving data
stored in a relational database.
• SQL was the first commercial language introduced for
E.F. Codd’s Relational Model
• Today almost RDMBS (MySQL, Oracle, Infomix, Sybase,
MS Access) uses SQL as the standard database
language.
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3. SQL
• SQL functions fit into two broad
categories:
• Data Definition Language (DDL)
• Data Manipulation language (DML)
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4. DATA DEFINITION LANGUAGE
• Data Definition Language (DDL) statements are used
to define the database structure or schema.
• All DDL commands are auto-committed. That means it
saves all the changes permanently in the database.
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5. DDL COMMANDS
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COMMAND DESCRIPTION
CREATE To create new table or database
ALTER For alteration
TRUNCATE Delete data from table
DROP To drop a table
RENAME To rename a table

6. CREATE Command
• CREATE is a DDL command used to create a table or
database.
• Following is the syntax:
CREATE DATABASE database_name
Example:
CREATE DATABASE Books
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7. CREATE Command
Syntax
CREATE TABLE table_name
(Column_name datatype[(size)] primary key,
Column_name datatype[(size)],
)
Example
CREATE TABLE AUTHORS
(au_id varchar(5) primary key,
au_fname varchar(50),
au_lname varchar(50),
phone varchar(20), ….. Note: copy the attribute from previous act
);
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8. ALTER Command
ALTER TABLE - ADD Column
To add a column in a table, use the following syntax:
ALTER TABLE table_name
ADD column_name datatype;
ALTER TABLE Customers
ADD Email varchar(255);
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9. ALTER Command
ALTER TABLE - DROP Column
To delete a column in a table, use the following syntax (notice
that some database systems don't allow deleting a column):
ALTER TABLE table_name
DROP COLUMN column_name;
ALTER TABLE Authors
DROP COLUMN Email;
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10. ALTER Command
ALTER TABLE - DROP Column
To delete a column in a table, use the following syntax (notice
that some database systems don't allow deleting a column):
ALTER TABLE table_name
DROP COLUMN column_name;
ALTER TABLE Authors
DROP COLUMN Email;
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11. Thank you
Mirjam Nilsson​
mirjam@contoso.com
www.contoso.com