This document discusses SQL and its data types, data definition language (DDL), data manipulation language (DML), and data control language (DCL). It defines SQL as a standardized language for querying and updating databases and lists common SQL data types like string, numeric, and date/time. It describes DDL commands for creating, altering, and dropping database tables as well as adding, modifying, and removing columns.

1. Contents
1. SQL data type
2. Data Definition Language(DDL)
3. Data Manipulation Language(DML)
4. Data Control Language(DCL)

2. 1. SQL data type
1. SQL
▪ Structured Query Language(SQL) was designed by IBM to
create a standardize structure for interrogating and updating
databases.
▪ High-level language: “what to do” rather than “how to do it.”
- Avoid a lot of data-manipulation details needed in
procedural languages like c++ or java.

3. 1. SQL data type
1. SQL
◆ SQL data types (from Oracle 9i):
▪ String types
Char(n) – fixed-length character data, n characters long maximum length
= 2000 bytes
Varchar2(n) – variable length character data, maximum 4000 bytes
Long – variable-length character data, up to 4gb. Maximum 1 per table
▪ Numeric types
Number(p,q) – general purpose numeric data type
Integer(p) – signed integer, p digits wide
Float(p) – floating point in scientific notation with p binary digits precision
▪ Data/Time types
Date – fixed-length date/time in dd-mm-yy form

4. 2. Data Definition Language(DDL)
◆ Characteristic:
▪ Allows the dba or user to describe and name entities, attributes.
▪ Relationships required for the application and any associated
integrity and security constraints.
▪ Commands define a database, including
creating, altering, dropping tables and establishing constraints.

5. 2. Data Definition Language(DDL)
◆ Characteristic:
▪ Create a table
Create table [table name] ( columnname datatype, ...);
For example:
Create table customers ( col1 number, col2 varchar2(20));
▪ Rename a table
Alter table [table name] rename to [new table name];
For example:
Alter table customers rename to customer;
▪ Add a column
Alter table [table name] add ( [column name] [datatype], ... );
For example:
Alter table employee add (id int);

6. 2. Data Definition Language(DDL)
◆ Characteristic:
▪ Modify a column
Alter table [table name] modify ( [column] [new data type] );
For example:
Alter table employee modify( sickhours float );
▪ Drop a column
Alter table [table name] drop column [column name];
For example:
Alter table employee drop column vacationpay;
▪ Removing tables
Drop table statement allows you to remove tables from your
schema:
Drop table employee