Technology Questions

Aggregate functions in SQL are used to perform calculation on data. These functions are inbuilt in SQL and return a single value.

SUM( )

SUM function returns the sum or addition of all NOT NULL values of a column. For e.g. I have a Table employee with the fields id, name, salary and I want the sum of all salaries, I can use SUM function as shown
SELECT SUM(emp_salary) from employee;
Hence, if my column emp_salary has values 20,000, 22,000, 21,000; the output will be 63,000

AVG( )

 
AVG function returns the average of all NOT NULL values of a column. For e.g. I have a Table employee with the fields id, name, salary and I want the average of all salaries, I can use AVG function as shown
SELECT AVG(emp_salary) from employee;
Hence, if my column emp_salary has values 20,000, 22,000, 21,000; the output will be 21,000

COUNT( )

COUNT function returns the number of rows or values of a table. For e.g. I have a Table employee with the fields id, name, salary and I want the count of all rows, I can use COUNT function as shown
SELECT COUNT(*) from employee;

Max ( ) and Min ( )

MAX function returns the largest value of a column in a table. For e.g. I have a Table employee with the fields id, name, salary and I want the maximum salary of an employee, I can use MAX function as shown
SELECT MAX(emp_salary) from employee;
Hence, if my column emp_salary has values 20,000, 22,000, 21,000; the output will be 22,000

MIN function returns the smallest value of a column in a table. For e.g. I have a Table employee with the fields id, name, salary and I want the minimun salary of an employee, I can use MIN function as shown
SELECT MIN(emp_salary) from employee;
Hence, if my column emp_salary has values 20,000, 22,000, 21,000; the output will be 20,000

CompareValidator  allows checking if data of one control match with other control

- If the table structure is changed ( a field is added ), the program will have to be modified.

- Program might retrieve the columns which it might not use, leading on I/O over head.

- The chance of an index only scan is lost.

C++ is created by Bjarne Stroustrup of AT&T Bell Labs as an extension of C, C++ is an object-oriented computer language used in the development of enterprise and commercial applications. Microsoft’s Visual C++ became the premier language of choice among developers and programmers.

TelephonyManager class can be used to get the IMEI number. It provides access to information about the telephony services on the device.

Code

        TelephonyManager mTelephonyMgr = (TelephonyManager)

        getSystemService(Context.TELEPHONY_SERVICE);

        String imei = mTelephonyMgr.getDeviceId();

Recursive query can be create in SQL using stored procedure but you can also use CTE (Common table expression). It might be also worth asking about performance as CTE is not always very fast.

The purpose of garbage collection is to identify and discard those objects that are no longer needed by the application, in order for the resources to be reclaimed and reused.

Once can use the Shell function to call any Aplication in VB 6.0. For Outlook Express one can use, Shell (msimn.exe)