The second Lab

1. SQL Database Language
Lab2: SQL Commands DDL & DML

2. DDL Commands
 DDL statements are used to build and modify the
structure of your tables and other objects in the
database.
 CREATE – Creates objects in the database
 ALTER – Alters objects of the database
 DROP – Deletes objects of the database
 TRUNCATE – Deletes all records from a table and resets table
identity to initial value.
 When you execute a DDL statement, it takes effect
immediately.

3. DDL Commands – CREATE TABLE
 The CREATE TABLE statement is used to
create a table in a database.
CREATE TABLE table_name
(
column_name1 data_type(size),
column_name2 data_type(size),
column_name3 data_type(size),
....
);

4. DDL Commands – Data Types
Data Type Description
VARCHAR2(SIZE)
Where size is the number of characters to store.
Variable-length string.
CHAR(SIZE)
Where size is the number of characters to store. Fixed-
length strings. Space padded.
NUMBER(P,S)
Where p is the precision and s is the scale.
For example, number(7,2) is a number that has 5 digits
before the decimal and 2 digits after the decimal.
DECIMAL(P,S) Where p is the precision and s is the scale.
INT Integer value
DATE Stores year, month, and day values(DD-MON-YY)
TIMESTAMP Stores year, month, day, hour, minute, and second values

5. DDL Commands – Large Objects Data
Types
 Large Objects (LOBs) are a set of data types that
are designed to hold large amounts of data.
 An LOB can hold up to a maximum size ranging
from 8 terabytes to 128 terabytes depending on
how your database is configured.
 Storing data in LOBs enables you to access and
manipulate the data efficiently in your application.
Refer
to
this
site
for
more
information
(Oracle
Documentation):
https://docs.oracle.com/cd/E18283_01/appdev.112/e18294/adlob_intro.ht
m

6. DDL Commands – Large Objects Data
Types
Large Object
(LOB) Data Type
Description
BLOB
Binary Large Object
Stores any kind of data in binary format. Typically used for
multimedia data such as images, audio, and video.
CLOB
Character Large
Object
Stores string data in the database character set format. Used for
large strings or documents that use the database character set
exclusively. Characters in the database character set are in a fixed
width format.
NCLOB
National Character
Set Large Object
Stores string data in National Character Set format. Used for large
strings or documents in the National Character Set. Supports
characters of varying width format.
BFILE
External Binary File
A binary file stored outside of the database in the host operating
system file system, but accessible from database tables. BFILEs
can be accessed from your application on a read-only basis.
Use BFILEs to store static data, such as image data, that is not
manipulated in applications.
Refer
to
this
site
for
more
information
(Oracle
Documentation):
https://docs.oracle.com/cd/E18283_01/appdev.112/e18294/adlob_intro.ht
m

7. DDL Commands – CREATE TABLE
 Example on CREATE TABLE:

8. DDL Commands – ALTER TABLE
 The ALTER TABLE statement is used to add,
delete, or modify columns in an existing table. It is
also used to rename a table or a column.
 To add a column in a table, use the following
syntax:
ALTER TABLE table_name
ADD column_name datatype

9. DDL Commands – ALTER TABLE
 To modify the data type of a column in a table, use the
following syntax, also you can modify more than one column
at once.
ALTER TABLE table_name
MODIFY column_name datatype
ALTER TABLE table_name
MODIFY (column_name1 datatype,
column_name2 datatype,
………………..
column_nameN datatype);
Modify single column Modify multiple columns

10. DDL Commands – ALTER TABLE
 To delete a column in a table, use the following
syntax
ALTER TABLE table_name
DROP COLUMN column_name

11. DDL Commands – ALTER TABLE
 To rename a column or a table , use the following
syntax:
ALTER TABLE table_name
RENAME COLUMN old_name to
new_name;
ALTER TABLE table_name
RENAME TO new_table_name;
Rename a column
Rename a table

12. DDL Commands – DROP TABLE
 DROP TABLE statement allows you to delete a
table from the SQL database.
DROP TABLE table_name;

13. DDL Commands – Constraints
 SQL constraints are used to specify rules
for the data in a table.
 If there is any violation between the
constraint and the data action, the action is
aborted by the constraint.
 Constraints can be specified when the table
is created (in a CREATE TABLE statement)
or after the table is created (in an ALTER
TABLE statement).

14. Adding / Deleting Constraints
 There are two ways of adding
constraints:
◦ Within table creation
◦ Using ALTER query
CREATE TABLE student(
ID Number(8),
CPR Number(9),
Name Varchar2(15),
GPA Number(3,2),
Major Varchar2(5) Not Null,
Year INT Default 1,
PRIMARY KEY (ID),
UNIQUE (CPR) );
CREATE TABLE table_name
(
column_name1 data_type(size) constraint_name,
column_name2 data_type(size) constraint_name,
column_name3 data_type(size) constraint_name,
....
);

15. Adding / Deleting Constraints
ALTER TABLE student
ADD CONSTRAINT student_id_pk PRIMARY KEY (id);
ALTER TABLE student
ADD CONSTRAINT student_cpr_un UNIQUE (cpr);
ALTER TABLE student
MODIFY major NOT NULL;
ALTER TABLE student
MODIFY year DEFAULT 1;

16.  Using ALTER query
ALTER TABLE table_name
DROP CONSTRAINT constraint_name;
ALTER TABLE student
DROP CONSTRAINT student_id_pk;
Adding / Deleting Constraints

17.  Constraints can be enabled or
disabled instead of dropping and
adding again.
Enabling / Disabling
Constraints
ALTER TABLE table_name
DISABLE CONSTRAINT constraint_name;
ALTER TABLE student
DISABLE CONSTRAINT student_id_pk;
ALTER TABLE table_name
ENABLE CONSTRAINT constraint_name;
ALTER TABLE student
ENABLE CONSTRAINT student_id_pk;

18. DDL Commands – Constraints- NOT
NULL
 The NOT NULL constraint enforces a column to
NOT accept NULL values.
 The NOT NULL constraint enforces a field to
always contain a value. This means that you
cannot insert a new record, or update a record
without adding a value to this field.

19. DDL Commands – Constraints- UNIQUE
 The UNIQUE constraint uniquely identifies each
record in a database table.
 The UNIQUE and PRIMARY KEY constraints both
provide a guarantee for uniqueness for a column or
set of columns.
 A PRIMARY KEY constraint automatically has a
UNIQUE constraint defined on it.
 Note that you can have many UNIQUE constraints
per table, but only one PRIMARY KEY constraint.

20. DDL Commands – Constraints- PRIMARY
KEY
 The PRIMARY KEY constraint uniquely identifies
each record in a database table.
 Primary keys must contain UNIQUE values.
 A primary key column cannot contain NULL values.
 Most tables should have a primary key, and each
table can have only ONE primary key.

21. DDL Commands – Constraints- FOREIGN
KEY
 A FOREIGN KEY in one table
points to a PRIMARY KEY in
another table.
 The FOREIGN KEY constraint is
used to prevent actions that
would destroy links between
tables.
 The FOREIGN KEY constraint
also prevents invalid data from
being inserted into the foreign
key column, because it has to be
one of the values contained in
the table it points to.
DEPT table
EMP table
Primary Key
Foreign Key

22. DML Commands – INSERT INTO
 The INSERT INTO statement is used to insert new
records in a table.
INSERT INTO table_name
VALUES (value1,value2,value3,...);
INSERT INTO table_name (column1,column3,column6,...)
VALUES (value1,value3,value6,...);
 It is also possible to only insert data in specific
columns.

23. DML Commands – UPDATE
 The UPDATE statement is used to update existing
records in a table.
UPDATE table_name
SET column1=value1,column2=value2,...
WHERE some_column=some_value;
 NOTE: The WHERE clause specifies which record or records that should be
updated. If you omit the WHERE clause, all records will be updated!

24. DML Commands – DELETE
 The DELETE statement is used to delete rows in a table.
DELETE FROM table_name
WHERE some_column=some_value;
 NOTE: The WHERE clause specifies which record or records that should be
deleted . If you omit the WHERE clause, all records will be deleted!
 It is possible to delete all rows in a table without deleting the
table.
DELETE FROM table_name;