chapter -4 update,delete,alter,rename,create,insert,drop

8/6/2019 Chapter -4 Update,Delete,Alter,Rename,Create,Insert,Drop

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DATABASE MANAGEMENT

SYSTEMS


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OBJECTIVES

Creating a Table from a Table using CREATEstatement.

Inserting Data into a Table from another Table

using INSERT statement.

Delete Operations Updating the contents of a table

Modifying the Structure of Table

Renaming Table

Truncating Table

Destroying Table

2


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CREATING ATABLE FROM ATABLE USING

CREATE STATEMENT.

3

The Source table is a table identified in the SELECTsection of this SQL sentence. The Target table is one

identified in the CREATE section of this SQL sentence.

This table sentence populates the Target table with data

from the Source table.

To create a Target table without the records from thesource table (i.e. create the structure only), the select

statement must be a have a WHERE clause. The

WHERE clause must specify the condition that

cannot be satisfied.

Syntax: CREATE TABLE (, ,

) AS SELECT , ,

FROM


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CREATING ATABLE FROM ATABLE USING

CREATE STATEMENT.

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Example:

y create table d10history as select

empno,ename,job,hiredate,sal from

emp;

y create table empstruct as select

empno,ename,job,hiredate,sal from

emp where 1=2;

y create table empspec(eno,empname,

designation,salary) as select

empno,ename,job,sal from emp;


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INSERTING DATA INTOATABLE FROM ANOTHER

TABLE USING INSERT STATEMENT.

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To insert data one row at a time into a table, it

is quite possible to populate a table with data

that already exists in another table.

Here the WHERE clause is optional. If you arenot specify the WHERE clause then all the

from source table to target table is copied.

Syntax: INSERT INTO

SELECT , , FROM < TableName> [WHERE

];


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INSERTING DATA INTOATABLE FROM ANOTHER

TABLE USING INSERT STATEMENT.

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Example:

y insert into empstruct select

empno,ename,job,hiredate,sal from emp

where dpetno = 10 or job = AssistantProfessor;

Syntax: INSERT INTO

SELECT , ,

FROM < TableName> [WHERE ];


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DELETE OPERATIONS

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The DELETE command deletes rows from the

table that satisfies the condition provided by its

WHERE clause, and returns the number of

records deleted.

Removal of All Rows:.Syntax: DELETE FROM ;

Example: Empty the emp table.

DELETE FROM empstruct;

Removal ofSpecific Rows:Syntax: DELETE FROM WHERE

;

Example: DELETE FROM empstruct WHERE job =

Assistant Professor;


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UPDATING THE CONTENTS OF A TABLE

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The UPDATE command is used to change or modify

data values in table.

Updating of All Rows:

Syntax: UPDATE SET = , =

;

Example: UPDATE d10history SET deptno = 20, job

=Professor;

Updating of Records Conditionally:

Syntax: UPDATE SET =

, =

WHERE ;Example: UPDATE empspec SET empname=Ajay

Patel, designation=Assistant Professor where

eno = e001;


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MODIFYING THE STRUCTURE OF TABLE

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The structure of a table can be modified by usingALTER TABLE command.

ALTER TABLE allows changing the structure of an

existing table.

With ALTER TABLE it is possible to add or delete

columns, change the data type of existing columns.

Restrictions on the ALTER TABLE:

The following tasks cannot be performed when

using the ALTER TABLE clause:

y Change the name of the table.

y Change the name of the column.

y Decrease the size of a column if table data exists


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Adding New Columns:

Syntax: ALTER TABLE ADD

(

(),

() , );Example:

ALTER TABLE emp ADD(spouse

varchar2(40));

ALTER TABLE emp ADD(addressvarchar2(250),city varchar2(50));


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Dropping a Column from a Table:Syntax: ALTER TABLE DROP

COLUMN ;

Example: ALTER TABLE emp DROP COLUMN

spouse;

Modifying Existing Columns:

Syntax: ALTER TABLE MODIFY

(

());Example: ALTER TABLE emp MODIFY(empno

varchar2(20));

ALTER TABLE emp MODIFY(sal

number(9,2),job varchar2(50));


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RENAMING TABLE

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Oracle allows renaming of tables. Therename operation is done atomically,

which means that no other thread can

access any of the tables while the rename

process is running.

Syntax: RENAME TO

;

Example: RENAME d10history TO d10;


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TRUNCATING TABLE

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TRUNCATE TABLE empties a table completely.

Logically, this is equivalent to a DELETE

statement that deletes all rows, but there are

practical differences under some circumstances.

TRUNCATE TABLE differs from DELETE in the

following ways:

y Truncate operations drop and re-create table,

which is much faster than deleting rows one by

one.

y Truncate operations are not transaction-safe

(i.e. an error will occur if an active transaction

or an active table lock exists).

y The numbers of deleted rows are not returned.

Syntax: TRUNCATE TABLE ;

Example: TRUNCATE TABLE da;


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DESTROYING TABLE

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Sometimes tables within a particular

database become obsolete and need to bediscarded. In such situation using DROP

TABLE statement with the table name

can destroy a specific table. If a table is

dropped all records held within it are lostand cannot be recovered.

Syntax:

DRO

P TABLE;Example: DROP TABLE da;


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Thank You

chapter -4 update,delete,alter,rename,create,insert,drop

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