edited by
12,381 views
37 votes
37 votes

Consider a database table T containing two columns $\text{X}$ and $\text{Y}$ each of type $\text{integer}$. After the creation of the table, one record $\text{(X=1, Y=1)}$ is inserted in the table.

Let $\text{MX}$ and $\text{MY}$ denote the respective maximum values of $\text{X}$ and $\text{Y}$ among all records in the table at any point in time. Using $\text{MX}$ and $\text{MY}$, new records are inserted in the table $128$ times with $\text{X}$ and $\text{Y}$ values being $\text{MX+1, 2*MY+1}$ respectively. It may be noted that each time after the insertion, values of $\text{MX}$ and $\text{MY}$ change.

What will be the output of the following SQL query after the steps mentioned above are carried out?

SELECT Y FROM T WHERE X=7;
  1. $127$
  2. $255$
  3. $129$
  4. $257$
edited by

4 Answers

Best answer
48 votes
48 votes
$X = 1, Y = 1$

$X = 2, Y = 2\times 1 +1 = 3$

$X = 3, Y = 2\times 3 + 1 = 7$

$X = 4, Y = 2\times 7 + 1 = 15$

$X = 5, Y = 2\times 15 + 1 = 31$

$X = 6, Y = 2\times 31+1 = 63$

$X = 7, Y = 2\times 63 + 1 = 127$

Correct Answer: $A$
edited by
20 votes
20 votes

OPTION A is the answer

if you do this as mentioned by Arjun sir then you will get the answer 

$X = 1, Y = 1$

$X = 2, Y = 2*1 +1 = 3$

$X = 3, Y = 2*3 + 1 = 7$

$X = 4, Y = 2*7 + 1 = 15$

$X = 5, Y = 2*15 + 1 = 31$

$X = 6, Y = 2*31+1 = 63$

$X = 7, Y = 2*63 + 1 = 127$

but if this question will be extended to $X=$ $'N'$ value then if you observe the pattern then it will come out as

$Y=2^{N}-1$ and here it is asked for $X=7$ so if we put $X$ value then we will get $(2^{7}- 1= 128-1=127)$

Suppose if they asked for $X=128$ then $Y=2^{128}-1$ is the answer.

edited by
0 votes
0 votes

MY is simply doing the shift of the previous number in binary to left and adding 1 in LSB. So, after 6 additions to table, MX will be 7 and there will be seven 1's in MY which is equivalent to 2^8-1 in decimal.

0 votes
0 votes

After inserting 4 values we can interpret that its forming a series were elements next to it are found by adding powers of 2.

Interpreting it as a series is helpful because if the query would ask for any value of x greater than 10 then individual substitution will be time consuming. 

See the solution below for more understanding 

Hence option A is Answer (i.e 127) 

Answer:

Related questions

37 votes
37 votes
1 answer
1
go_editor asked Sep 29, 2014
12,599 views
Database table by name $\text{Loan_Records}$ is given below.$$\begin{array}{|c|c|c|} \hline \textbf {Borrower} & \textbf {Bank_Manager} &\textbf {Loan_Amount} \\\hline \...
40 votes
40 votes
6 answers
2
53 votes
53 votes
4 answers
3