Android History

Android inc. was founded in Palo Aulto,California,US by Andy Rubin,Rich Miner,Nicker Seaers and CHris WHite, in October 2003. Google acquired Android Inc. in August 2005.\


Android Beta SDK Released in 12 November 2007.


Android 1.0: The firest android device the HTC Dream(G1),featuring Android1.0. 23 sep 2008.

• Integration with Google services
• Web browser to show, zoom and pan full HTML and XHTML webpages,multiple pages show as windows
• Android Market app downloads and Updates
• Multitasking,Instant Messaging, WiFi and Bluetooth.

Android1.1 update for Android was released for T-Mobile G1 only. 9 th feb 2009.

Android1.5:(Cupcake) based on Linux kernel 2.6.27, 30th april 2009.

• Faster camera startup and Image capture.
• Much faster acquisition of GPS location(power by SUPL AGPS).
• On screen soft keyboard.
• Directly upload videos to you tube and picassa.

Android 1.6(Donut): based on Linux kernel 2.6.29, 15th sep 2009.

• Quick search box and voice search
• integrated camera, camcorder, and gallery, toggle between still and video capture modes
• battery usage indicator
• CDMA Support
• Multilingual text to speech function

Android 2.0(Eclair): based on Linux kernel 2.6.29, 26th october 2009.

• Multiple accounts for email and contact synchronization
• Microsoft exchange support for sync of email
• Bluetooth 2.1 support
• new browser user interface and support HTML5
• new calendar features

Android 2.0.1 SDK was released on 3 December 2009.

Android 2.1 SDK was released on 12 January 2010.

Android 2.2(Froyo): based on Linux kernel 2.6.32 on 20 may 2010.

• New tips widget for homescreen.
• improved exchange support.
• Hotspot support
• Multiple keyboard languages
• Adobe FLash 10.1

Android 2.3(Gingerbread): based on Linux kernel 2.6.35,  6 December 2010.

• UI refinements for simplicity and speed
• New keyboard for faster text input
• One touch woed selection and copy/paste
• Near field communication(NFC)
• Intenet Calling.

Android 3.0(Honeycomb): based on Linux kernel 2.6.36 for tablets on 22 february 2011. version 3.1SDK released on 10 may 2011. SDK 3.2 was released on 18 july 2011.

• Specially optimized for tablets and devices with larger screen sizes.
• Refined multitasking, rich notifications, home screen customization, widgets.
• Bluetooth tethering
• Built in support for media/picture transfer protocol

Android 4.0(Ice Creame Sandwich): Released on 19 oct 2011.

• New type interface called Roboto.
• New Face Unlock feature
• Android Beam- A secuer NFC powered content sharing platform.
• Re arrangeable folders,favourites Tray, screenshots.
• Swipe to dismiss notifications,tasks,and browsers tabs
• WI-FI Direct and Bluetooth HDP support.

Constraints in Oracle

Constraints:

Data integrity of the database must be maintained. In order to ensure data has integrity we have to implement certain rules or constraints. As these constraints are used to maintain integrity they are called as integrity constraints.

Constraints can be given at two different levels. If the constraint is related to a single column the constraint is given at the column level otherwise constraint is to be given at the table level. Base on the where a constraint is given, constraint are of two types:

1. Column Constraints
2. Table Constraints

Column Constraint:

A constraint given at the column level is called as Column Constraint. It defines a rule for a single column. It cannot refer to column other than the column at which it is defined. A typical example is PRIMARY KEY constraint when a single column is the primary key of the table.

Table Constraint:

A constraint given at the table level is called as Table Constraint. It may refer to more than one column of the table. A typical example is PRIMARY KEY constraint that is used to define composite primary key. A column level constraint can be given even at the table level, but a constraint that deals with more than one column must be given only at the table level. The following is the syntax of CONSTRAINT clause used with CREATE TABLE and ALTER TABLE commands.

[CONSTRAINT constraint] { [NOT] NULL | {UNIQUE | PRIMARY KEY} | REFERENCES [schema.] table [(column)] [ON DELETE CASCADE] | CHECK (condition) }

The following is the syntax of table constraint.

[CONSTRAINT constraint] { {UNIQUE | PRIMARY KEY} (column [,column] ...) | FOREIGN KEY (column [,column] ...) REFERENCES [schema.] table [(column [,column] ...)] [ON DELETE CASCADE] | CHECK (condition) }

The main difference between column constraint and table constraint is that in table constraint we have to specify the name of the column for which the constraint is defined whereas in column constraint it is not required as constraint is given on immediately after the column.

Creating Integrity Constraints
In the following few sections we will see how to integrity constraints.
NOT NULL Constraint:
Used to prevent any null value from entering into column. This is automatically defined forcolumn with PRIMARY KEY constraint.
CREATE TABLE COURSES( ...,name varchar2(20) CONSTRAINT courses_name_nn NOT NULL,.. );
CONSTRAINT option is used to given a name to constraint. The convention followed here is TABLENAME_COLUMN_TYPE.


PRIMARY KEY Constraint This constraint is used to define the primary key of the table. A primary key is used to uniquely identify rows in a table. There can be only one primary key in a table. It may consist of more than one column. If primary key is consisting of only one column, it can be given as column constraints otherwise it is to be given as table constraint. 
Note: You have to use table constraint to define composite primary key. Oracle does the following for the column that has PRIMARY KEY constraint .Creates a unique index to enforce uniqueness. 
CREATE TABLE COURSES( ccode varchar2(5) CONSTRAINT courses_pk PRIMARY KEY,... );
The following example shows how to define composite primary key using PRIMARY KEY constraint at the table level.
CREATE TABLE COURSE_FACULTY( ...,CONSTRAINT COURSE_FACULTY_PK PRIMARY KEY (ccode,faccode) );


UNIQUE Constraint Enforces uniqueness in the given column(s). Oracle automatically creates a unique index for this column.
CREATE TABLE courses ( ... ,name varchar2(20) CONSTRAINT courses_name_u UNIQUE, ... );
If two or more columns collective should be unique then UNIQUE constraint must be given at the table level.


FOREIGN KEY Constraint A foreign key is used to join the child table with parent table. FOREIGN KEY constraint is used to provide referential integrity, which makes sure that the values of a foreign key are derived from parent key. It can be defined either at the table level or at the column level. If a foreign key is defined on the column in child table then Oracle does not allow the parent row to be deleted, if it contains any child rows. However, if ON DELETE CASCADE option is given at the time of defining foreign key, Oracle deletes all child rows while parent row is being deleted.
CREATE TABLE course_faculty (ccode varchar2(5) CONSTRAINT course_faculty_ccode_fk REFERENCES courses(ccode), ... );
Note: When the name of the column in the referenced table is same as the foreign key then column need not be given after the table name. It means REFERENCES courses in the above example will suffice.
Table level constraint is used when foreign key is a composite foreign key.


ON DELETE CASCADE option As mentioned earlier, after a foreign key is defined, Oracle will NOT allow any parent row to be deleted if it has dependent rows in the child table. For example, if CCODE in COURSE_FACULTY table is defined as foreign key referencing CCODE column of COURSES table then it is NOT possible to delete rows from COURSES table if dependent rows exists in COURSE_FACULTY table. However, by using ON DELETE CASCADE it is possible to delete all child rows while parent row is being deleted.
CREATE TABLE course_faculty (ccode varchar2(5)CONSTRAINT course_faculty_ccode_fk REFERENCES courses(ccode) ON DELETE CASCADE, ..  );


CHECK Constraint Defines the condition that should be satisfied before insertion or updation is done.The condition used in CHECK constraint may NOT contain: A reference to pseudo column SYSDATE Subquery If it is given as column constraint, it can refer only to current column. But if it is given as table constraint, it can refer to more than one column of the table. In neither case it can refer to a column of other tables. The following example shows how to create CHECK constraint to make sure GRADE column of COURSE_FACULTY contains letters A, B and C only.
CREATE TABLE course_faculty( ..., grade char(1) CONSTRAINT course_faculty_grade_chk CHECK ( grade in (‘A’,’B’,’C’) ), ... );
The above CHECK constraint does not allow any other characters other than A, B and C. It must be noted that character comparison is always case sensitive. So to ignore case differences you can convert GRADE to uppercase before comparison made as follows:
CREATE TABLE course_faculty ( ..., grade char(1) CONSTRAINT course_faculty_grade_chk
CHECK ( upper(grade) in (‘A’,’B’,’C’) ), ... );
The following is an example of CHECK constraint at table level. The constraint makes sure the starting date (STDATE) of a batch is less than or equal to ending date (ENDDATE) of the batch.
CREATE TABLE batches ( ..., CONSTRAINT batches_dates_chk CHECK ( stdate <= enddate), );

SQL Operators

SQL Operators:

Apart from standard relational operators (= and >), SQL has some other operators that can

be used in conditions.

BETWEEN value-1 AND value-2 Checks whether the value is in the given range including the min and max values. This supports DATE type data also.The range is inclusive of the given values.

IN(list) Checks whether the value is matching with any one of the values given in the list. List contains values separated by comma(,). If the value is matching with any of the values given in the list then condition is taken as true.

LIKE pattern Checks whether the given string is matching with the given pattern.This operator is used to search for values when the exact value is not known. It selects rows that match the given pattern. The pattern can contain the following special characters.

IS NULL and IS NOT NULL Checks whether the value is null or not null.

To display the list of course where DURATION is in the range 20 to 25 days, enter:

select name from courses where duration between 20 and 25;

NAME

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

Oracle database

C programming

Java Language

Note: BETWEEN.. AND is alternative to using >= and <= operators.

The following command will retrieve all courses where duration is either 20 or 30 days.

select name from courses where duration in (20,30);

NAME

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

VB.NET

C programming

The same condition can be formed even without IN operator using logical operator OR as follows:

Select name from courses where duration = 20 or duration = 30;

However, it will be more convenient to user IN operator compared with multiple conditions compared with OR operator.

% Zero or more characters can take the place of %. _ (underscore) Any single character can take the place of underscore. But there must be one letter. To select the courses where the course name contains pattern .NET, enter:

select name,duration, fee from courses where name like '%.NET%'

NAME DURATION FEE

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

VB.NET 30 5500

ASP.NET 25 5000

The following example selects courses where second letter in the course code is “b” and column PREREQUISITE contains word “programming”.

select * from courses where ccode like '_b%' and prerequisite like '%programming%';

CCODE NAME DURATION FEE PREREQUISITE

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

vbnet VB.NET 30 5500 Windows and programming

Remember LIKE operator is case sensitive. 

For example the following SELECT command will select all the courses where the column FEE is null.

select * from courses where fee is null;

Though Oracle provides NULL keyword, it cannot be used to check whether the value of a column is null. For example, the following condition will always be false as Oracle treats two null values as two different values.

select * from courses where fee = null;

The above command does NOT work as fee though contains null value will not be equal to NULL. SO, we must use IS NULL operator.

Selecting distinct values:

DISTINCT clause of SELECT command specifies only distinct values of the specified column must be selected. The following SELECT command will display only distinct course fee values from COURSES

table.

select distinct fee from courses;

FEE

---------

3500

4000

4500

5000

5500

Whereas the same query without DISTINCT clause will select the following. 

select fee from courses;

FEE

---------

4500

5500

3500

5000

4500

4000