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CS 522 - Database

Administration

DDLDr. Dongming Liang

http://class.svuca.edu/~d.liang/([email protected])

Silicon Valley University

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Agenda

Database objectsCreate table

Constraints

Alter/drop table

Other schema objects

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Database ObjectsObjects Description

Table Basic unit of storage; composed ofrows

View Logically represents subsets of data

from one or more table

Sequence Generates numeric values

Index Improves the performance of somequeries

Synonym Gives alternative name to an object

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DDL

DDL

(Data Definition Language)

CREATE

ALTER

DROP

TRUNCATE

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CREATE Table Statement

You must have CREATE Table privilege

A storage area

CREATE TABLE [schema.]table(column datatype[DEFAULT expr] [, ]);

You specify

Table name Column name, column data type, and column size

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Reference Another Users Table

Tables belonging to other users are notin the users schema

You should use the owners name as a

prefix to those tablesFor example, UserA wants to access the

EMPLOYEES table the belongs to UserB

SELECT *

FROM UserB.employees

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Default Option

When you define a table, you canspecify a default value for a columnduring an insert

hire_date DATE DEFAULT sysdate, Literal values, expressions, or SQL

functions are legal values

Another columns name or apseudocolumn are illegal values

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Example: Create Table

CREATE TABLE dept(deptno NUMBER(2),

dname VARCHAR2(14),

loc VARCHAR2(13),

create_date DATE

DEFAULT SYSDATE);

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Confirm Table Creation

DESCRIBE deptDESCRIBE dept

Name Null Type

---------------- ---- ------

DEPTNO NUMBER

DNAME VARCHAR2(14)LOC VARCHAR2(13)

CREATE_DATE DATE

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Data TypesData Type Description

VARCHAR2(size) Variable-length character dataCHAR(size) Fixed-length character data

NUMBER(p, s) Variable-length numeric data

DATE Data and time values

CLOB Character data (up to 4GB)

BFILE Binary data stored in an externalfile

ROWID The unique address of a row in itstable

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DatetimeData Types

Data Type Description

TIMESTAMP Date with fractional seconds

INTERVAL YEARTO MONTH

Stored as an interval of years andmonths

INTERVAL DAYTO SECOND

Stored as an interval of days,

hours, minutes, and seconds

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Constraints

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Including Constraints

Use constraints to prevent invalid dataentry into tables

Constraints enforce rules at the tablelevel

Constraints prevent the deletion of

table if there are dependencies

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Constraint Types

NOT NULL the column cannot contain a nullvalue

UNIQUE column value must be unique

PRIMARY KEY uniquely identify each row inthe table

FOREIGN KEY establish and enforce areferential integrity

CHECK specify a condition that must betrue

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Constraint Guidelines

You can name a constraint, or the Oracleserver generates a name by using theSYS_Cnformat

Create a constraint at either of the followingtimesAt the same time as the creation of the table

After the creation of the table

Define a constraint at the column or tablelevel

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Define Constraint

CREATE TABLE [schema.]table(column datatype[DEFAULT expr]

[column_constraint],

[table_constraint][, ]);

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Example: Define Constraint

CREATE TABLE employees(employee_id NUMBER(6)

CONSTRAINT emp_emp_id_pk

PRIMARY KEY,

first_name VARCHAR2(20),

);

Column level syntax

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Example: Define Constraint

CREATE TABLE employees

(employee_idNUMBER(6),


job_id VARCHAR2(10) NOT NULL,

CONSTRAINT emp_emp_id_pk

PRIMARY KEY(EMPLOYEE_ID));

Here emp_emp_id_pk is in table level syntax

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FOREIGN KEY

Aforeign keymeans that

values inone table must also

appear in another table.

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Define Foreign Key

CREATE TABLE employees(employee_idNUMBER(6),


dept_id NUMBER(4),

CONSTRAINT emp_dept_id_fk

FOREIGN KEY(dept_id)

REFERENCES departments(department_id));

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Foreign Key Constraint: Keywords

FOREIGN KEY: define the column in childtable

REFERENCES: identify the parent table andcolumn

ON DELETE CASCADE: delete the dependentrows in the child table when a row in theparent table is deleted

ON DELETE SET NULL: convert dependentforeign key values to null

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CHECK Constraint

Defines a condition that each row mustsatisfy

,

salary NUMBER(4)

CONSTRAINT emp_salary_min

CHECK(salary > 0),

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CHECK Constraint

The following expressions are notallowed

References to CURRVAL, NEXTVAL, LEVEL,

and ROWNUM pseudocolumns Calls to SYSDATE, UID, USER, and

USERENV functions

Queries that refer to other values in otherrows

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Violating Constraints

UPDATE employeesSET department_id = 55

WHERE department_id = 110;

Department 55 does not exist theparent table, DEPARTMENTS, and soyou receive a parent key not foundviolation ORA-02291 error.

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Create a Table Using a Subquery

CREATE TABLE dept80AS

SELECT employee_id, last_name,

salary*12 ANNSAL, hire_date

FROM employees

WHERE department_id = 80;

Be sure to provide a column alias, such asANNSAL, when selecting an expression

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Alter Table

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Alter Table Statement

Use theAlter Table statement to:Add a new column

Modify an existing column definition

Define a default value for the new column

Drop a column

Rename a column

Change table to read only status

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Read Only Tables

Use the Alter Table statement to put a tableinto read-only mode

Prevent DDL or DML changes during tablemaintenance

ALTER TABLE employees READ ONLY;

Change it back into read/write mode after themaintenance

ALTER TABLE employees READ WRITE;

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Drop a Table

Moves a table to the recycle binRemoves the table and all its data

entirely if the PURGE clause in specified

Invalidates dependent objects andremoves object privileges on the table

DROP TABLE dept80;

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Other Schema Objects

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from one or more tableSequence Generates numeric values

Index Improves the performance of some

queries


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View

You can present logical subsets orcombination of data by creating viewsof tables

A view is a logical table based on atable or another view

A view contains no data of its own, but

is like window through which data fromtables can be viewed or changed

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Base Table of View

The tableson which aview is

based arecalledbase

tables

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Advantages of Views

To restrict data accessTo provide data independence

To make complex queries easy

To present different views of the samedata

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Simple Views and Complex Views

Feature Simple Views Complex ViewsNumber oftables

One One or more

Containfunctions No Yes

Contain groupsof data

No Yes

DML operationsthrough a view

Yes Not always

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Create a View

CREATE VIEW empvu30AS

SELECT employee_id, last_name, salary

FROM employeesWHERE department_id = 30;

A view is stored as a SELECT statementin the data dictionary

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Retrieve Data from a View

You can retrieve data from a view as youwould from any table

SELECT *

FROM salvu50

You can display either the contents of theentire view or just specific rows and columns

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Create Complex View

Create a complex view that contains groupfunctions to display values from two tables:

CREATE OR REPLACE VIEW dept_sum_vu

(name, minsal, maxsal, avgsal)

AS SELECT d.department_name, MIN(e.salary),MAX(e.salary), AVG(e.salary)

FROM employees e, departments dWHERE e.department_id = d.department_id

GROUP BY d.department_name

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Remove a View

You can remove a view without losingdata because a view is based onunderlying tables in the database

DROP VIEW salvu50;

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queries


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Sequences

Can automatically generate uniquenumbers

Is a sharable object

Can be used to create a primary key

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Create a Sequence

Create a sequence name DEPT_DEPTID_SEQto be used for the primary key of theDEPARTMENTS table

CREATE SEQUENCE dept_deptid_seqINCREMENT BY 10START WITH 120MAXVALUE 9999

NOCACHENOCYCLE

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NEXTVAL and CURRVAL

NEXTVAL returns the next available sequencevalue

INSERT INTO departments(department_id,

department_name, location_id)

VALUES (dept_deptid_seq.NEXTVAL,

Support, 2500);

CURRVAL obtains the current sequence valueSELECT dept_deptid_seq.CURRVAL

FROM dual;

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queries


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How Are Indexes Created?

Automatically: a unique index is createdautomatically when you define aPRIMARY KEY or UNIQUE constraint in

a table definitionManually: Users can create nonunique

indexes on columns to speed up access

to the rows

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Create an Index

Improve the speed of query access tothe LAST_NAME column in theEMPLOYEES table

CREATE IDNEX emp_last_name_idx

ON employees (last_name);

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Index Creation Guidelines

Create an index when:A column contains a wide range of values

One or more columns are frequently used

together in a WHERE clause or a joincondition

The table is large and most queries are

expected to retrieve less than 2% to 4% ofthe rows in the table

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Remove an Index

Remove an index from the datadictionary by using the DROP INDEXcommand

For example, remove theemp_last_name_idxindex:

DROP INDEX emp_last_name_idx;

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queriesSynonym Gives alternative name to an object

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Synonym for an Object

Simplify access to objects by creating asynonym (another name for an object)

With synonyms you can

Create an easier reference to a table that isowned by another user

Shorten lengthy object names

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Create and Remove Synonyms

Create a shortened name for theDEPT_SUM_VU view

CREATE SYNONYM d_sum

FOR dept_sum_vu;

Drop a synonym

DROP SYNONYM d_sum;

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Summary

Categorize the main DB objects

Data types, table creation, and constraints

Create, use, and remove views

Automatically generate sequence number byusing sequence

Create indexes to improve speed of queryretrieval

Use synonyms to provide alternative namesfor objects

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Oracle Database Architecture

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