GATE IT 2004 | Question: 76

Question

A table T1 in a relational database has the following rows and columns: 
$$\begin{array}{|c|c|c|} \hline \text {Roll no. } & \text {Marks} \\\hline 1&  10 \\\hline 2 & 20 \\\hline3 & 30  \\\hline 4 & \text{NULL}\\\hline \end{array}$$
The following sequence of SQL statements was successfully executed on table T1.

Update T1 set marks = marks + 5
Select avg(marks) from T1

What is the output of the select statement?

• A. $18.75$
• B. $20$
• C. $25$
• D. $\text{Null}$

Comments

 

null  =  unknown 

unknown+5  =  unknown

 

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Expect for count all other aggregate functions will ignore null values and count counts the number of rows its not considered about the value within it it just counts and adds to the result if it remains after being filtered out by the where conditions

Answer 1

option a

Comments

Null values are ignored in SQL. They won't be assumed to have value 0.

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No. For avg, the count won't include null row.

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here the count ignore num values . beacuse it is calculated on MARKS right ?

If it would have count (Roll no) then it would return 4 rows right ?