Chapter -4 Update,Delete,Alter,Rename,Create,Insert,Drop
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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
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CREATING ATABLE FROM ATABLE USING
CREATE STATEMENT.
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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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MODIFYING THE STRUCTURE OF TABLE
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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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MODIFYING THE STRUCTURE OF TABLE
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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
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