TechnicalBits

These are Transaction Control Language (TCL) statements used to manage the changes made by DML statements.

Rollback:

This is used for undoing the work done in the current transaction. It will restore database to original state since the last COMMIT.This command also releases the locks if any hold by the current transaction. 
The command used in SQL for this is simply:

ROLLBACK;
All the transactions will be undone once we rollback.

Savepoint:
This is used for identifying a point in the transaction to which a programmer can later roll back. That is it is possible for the programmer to divide a big transaction into subsections each having a savepoint defined in it. 
The command used in SQL for this is simply:

SAVEPOINT savepointname;

For example:
UPDATE….. 

DELETE…. 

SAVEPOINT e1; 

INSERT…. 

UPDATE…. 

SAVEPOINT e2; …

It is also possible to define savepoint and rollback together so that programmer can achieve rollback of part of a transaction. Say for instance in the above

ROLLBACK TO SAVEPOINT e2;
This results in the rollback of all statements after savepoint e2

Commit:
This is used to end the transaction and make the changes permanent. When commit is performed all save points are erased and transaction locks are released. In other words commit ends a transaction and marks the beginning of a new transaction. 

This command used to make the database changes permanent(i.e.save work done).
we can't perform Roll Back once we commit the transaction.
The command used in SQL for this is simply:

COMMIT;

There are 4 types of SQL commands or statements in oracle as given below :
DDL
Data Definition Language (DDL) statements are used to define the database structure or schema. 
Some examples:
CREATE - to create objects like Table,Views,Sequences,Indexes,Synonyms etc. in the database
ALTER - alters the structure of the database
DROP - delete objects like Table,Views,Sequences,Indexes,Synonyms etc. from the database
TRUNCATE - remove all records from a table, including all spaces allocated for the records are removed
COMMENT - add comments to the data dictionary
RENAME - rename an object

DML
Data Manipulation Language (DML) statements are used for accessing and managing data within relational database tables. 
Some examples:
SELECT - retrieve data from the a database tables
INSERT - insert data into a table
UPDATE - updates existing data within a table
DELETE - deletes specific or all records from a table, the space for the records remain
MERGE - UPSERT operation (insert or update)
CALL - call a PL/SQL or Java subprogram
EXPLAIN PLAN - explain access path to data
LOCK TABLE - control concurrency


DCL
Data Control Language (DCL) statements are used to control privileges in database.
To perform any operation in database such as creating tables,views or perform insert,delete to table we need privileges.
Some examples:
GRANT - gives user's access privileges to database
REVOKE - withdraw access privileges given with the GRANT command

The operations for which privileges may be granted to or revoked from a user or role may include CONNECT, SELECT, INSERT, UPDATE, DELETE, EXECUTE, and USAGE.


TCL
Transaction Control Language (TCL) statements are used to manage the changes made by DML statements. 
It allows statements to be grouped together into logical transactions.
COMMIT - save work done
SAVEPOINT - identify a point in a transaction to which you can later roll back or return
ROLLBACK - restore database to original since the last COMMIT
SET TRANSACTION - Change transaction options like isolation level and what rollback segment to use

SQL DELETE Statement:
The DELETE command is used to remove rows from a table. A WHERE clause can be used to only remove some rows. If no WHERE condition is specified, all rows will be removed.It provides the facility of conditional-based deletion

Syntax to SQL DELETE:
DELETE FROM table_name [WHERE condition];

Eg. DELETE FROM CUSTOMER WHERE CUSTOMER_ID=107; 
(This will delete only one customer record whose id is 107)
OR DELETE FROM CUSTOMER; (This will delete the all customer records)

SQL TRUNCATE Statement:
TRUNCATE removes all rows from a table.The operation cannot be rolled back and no triggers will be fired.
TRUNCATE removes the record permanently.

Syntax to TRUNCATE a table:
TRUNCATE TABLE table_name;

Eg. TRUNCATE TABLE CUSTOMER; (This will delete all customer records)


SQL DROP Statement:
DROP command is a DDL command. It removes the information along with structure. It also removes all information about the table from data dictionary.
The DROP command removes a table from the database. All the tables' rows, indexes and privileges will also be removed. No DML triggers will be fired. 

Syntax to DROP a table:
DROP TABLE table_name;

Eg. DROP TABLE CUSTOMER; (This will delete all customer records also the table structure)

1.TRUNCATE ,DROP is a DDL command whereas DELETE is a DML command.
As such, DELETE operations can be rolled back (undone), while DROP and TRUNCATE operations cannot be rolled back.

2.TRUNCATE is much faster than DELETE.
Reason: When you type DELETE.all the data get copied into the Rollback Table-space first.then delete operation get performed.performed. Thats why when you type ROLLBACK after deleting a table ,you can get back the data(The system get it for you from the Rollback Table-space).All this process take time.But when you type TRUNCATE,it removes data directly without copying it into the Rollback Table-space. Thatswhy.Thatswhy TRUNCATE is faster.Once you Truncate you can't get back the data.

3.Drop command will delete the entire rows as well as the structure.But truncate will delete the contents only not the structure, so no need to give specifications for another table creation.

Let's consider below tabular form to demo this topic that is Emergency Contact Details.
Suppose that we have to access the all the Emergency Contact Names of the user Akshay Patil.

The Apex JavaScript API has some very convenient functions to access the values of page items.

For example, if you wante to access the contents of a text field with JavaScript, would need to reference it something like this:
$x("P7_TEXT_FIELD").value;
or
$("#P7_TEXT_FIELD").val();

If the item you want to reference is a display only item, then the syntax changes:
x = $("#P7_DISPLAY_ONLY").text();

If you need to set the values of these items, the you need to use the varying syntax as well:
$x("P7_TEXT_FIELD").value = "Hello World!";
or
$('#P7_TEXT_FIELD').val("Hello World!");
or
$("#P7_DISPLAY_ONLY").text("Hello World!");


Dealing with these various syntax constructs can be confusing. Fortunately the Apex JavaScript API makes this process much easier. To get page item values simply use $v(“<item_name>”):

x = $v("P7_TEXT_FIELD");
y = $v("P7_DISPLAY_ONLY");
To set the item values use:

$s("P7_TEXT_FIELD","Hello World!");
$s("P7_DISPLAY_ONLY","Hello World!");
See an example on my demo page.

The $v2() is handy if you need to access multiple items in an array. For example multiple selections from check boxes or from a shuttle control can be fetched as an array and handled that way in JavaScript:

myArr = $v2("P7_SHUTTLE_CONTROL");
for (idx=0; idx<myArr.length; idx++) {
  //do something with myArr[idx];
}

To set region width automatically perform following steps:

1. Set region id as shown below


2. Add following code in region header and footer block to set Scroll bar on overflow.

        <div style="overflow: auto;" >...</div>

3. Write dynamic action to set screen width to region.

Add below code in dynamic action :

var v_size = screen.width;
$('#dependent_data').width(v_size);

                3. Use the name shown in Inspect Element Window.

1. Use "Read Field" button in Report query window, it fill Fields variables with the fields of the query and avoid later problems.
2. The length of the field $F {name} shouldn't exceed 32 characters (field < 32).

1.       Download APEX4.2 from Oracle Site for Windows 32-bit.