SQL

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