GATE | Gate IT 2005 | Question 67

A company maintains records of sales made by its salespersons and pays them commission based on each individual\’s total sales made in a year. This data is maintained in a table with following schema:

salesinfo = (salespersonid, totalsales, commission)

In a certain year, due to better business results, the company decides to further reward its salespersons by enhancing the commission paid to them as per the following formula:

If commission < = 50000, enhance it by 2% 
If 50000 < commission < = 100000, enhance it by 4% 
If commission > 100000, enhance it by 6%

The IT staff has written three different SQL scripts to calculate enhancement for each slab, each of these scripts is to run as a separate transaction as follows:

T1	Update salesinfo Set commission = commission * 1.02 Where commission < = 50000;
T2	Update salesinfo Set commission = commission * 1.04 Where commission > 50000 and commission is < = 100000;
T3	Update salesinfo Set commission = commission * 1.06 Where commission > 100000;

Which of the following options of running these transactions will update the commission of all salespersons correctly

(A)

Execute T1 followed by T2 followed by T3

(B)

Execute T2, followed by T3; T1 running concurrently throughout

(C)

Execute T3 followed by T2; T1 running concurrently throughout

(D)

Execute T3 followed by T2 followed by T1

Answer: (D)
Explanation:

T3 followed by T2 followed by T1 

If this sequence is not followed then it may happen that the Officer of one slab gets benefited twice. 

Say an officer is having commission as 99,999, He must get an updated commission according to T2. But then 

99,999*1.04=1,03998 and he again becomes eligible for next slab of commission. 

T3 followed by T2 followed by T1 will be check all border cases like above.So Answer is D

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