Data Analyst Interview Questions

=COUNTIF(D4:D7,D4)

Use Pivot Table and select one variable in Row label and the other variable in Column label.

=MID (A2,1,FIND("",A2)-1)

The main difference between cluster and stratified sampling is that in stratified sampling all the strata need to be sampled. In cluster sampling one proceeds by first selecting a number of clusters at random and then sampling each cluster or conduct a census of each cluster. But usually not all clusters would be included.

In a linear regression model, there should be homogeneity of variance of the residuals. In other words, the variance of residuals are approximately equal for all predicted dependent variable values.

• WHERE statement can be used in procedures to subset data while IF statement cannot be used in procedures.
• WHERE can be used as a data set option while IF cannot be used as a data set option.
• WHERE statement is more efficient than IF statement. It tells SAS not to read all observations from the data set
• WHERE statement can not be used when reading data using INPUT statement whereas IF statement can be used.
• When it is required to use newly created variables, use IF statement as it doesn't require variables to exist in the READIN data set.

PROC MEANS DATA = dataset_name;
VAR analysis_variable;
CLASS grouping_variable;
RUN;

Detailed Explanation :PROC MEANS 


The NODUPKEY option removes duplicate observations where value of a variable listed in BY statement is repeated while NODUP option removes duplicate observations where values in all the variables are repeated.
The SQL procedure performed better with the smaller datasets whereas the data step performed better with the larger datasets (more than approx. 100 MB).
Without 'BY' statement, SAS will merge the 1st observation from dataset A and 1st observation from dataset B to form the 1st observation of the final dataset. It might lead to meaningless results.

There are 5 ways to create macro variables:

• %Let
• Iterative %DO statement
• Call Symput 
• Proc SQl into clause 
• Macro Parameters

Proc SQL;
select name as fullname from table1;
quit;

11. How to calculate percentile values with SAS?

We can use PROC MEANS or PROC UNIVARIATE to calculate percentile values. For example, specify options P10, P90 to calculate 10th and 90th percentile score. PROC MEANS cannot calculate custom percentile values such as 97.5th or 99.5th percentile. To calculate these custom percentile values, you can use PCTLPTS= option in PROC UNIVARIATE.

Tutorial : PROC UNIVARIATE

select
        case when sex='M' then 1 else 0 end as males
        , case when sex='F' then 1 else 0 end as females
    from sashelp.class;
quit;

2. What are the common SQL data types ?

Data	Type Format
Numeric	NUMBER(L,D), INTEGER,SMALLINT,DECIMAL(L,D)
Character	CHAR(L),VARCHAR(L)
Date	DATE

SELECT *
FROM PRODUCT
WHERE SALES > 200

4. Difference between WHERE and HAVING clauses

The HAVING clause comes into effect when GROUP BY is used. It runs after GROUP BY so it filters grouping variable. Whereas WHERE clause runs prior to GROUP BY clause so it does not filter a grouping variable.


5. Difference between Full Join and Cross Join?

A full join keeps all rows from both of the input tables even if we cannot find a matching row.
Cross Join returns cartesian product of tables. It matches every row of one table with every row of another table.

6. Difference between UNION and UNION ALL

The main use of UNION and UNION ALL is to join two tables. The main difference between them is that UNION removes duplicate records and UNION ALL keeps the duplicate records. By 'duplicate records', all the values of two or more rows are same.

7. How to create a blank table

Method I :

The following method creates a new table called temp2 with the same column names and attributes of table temp.

CREATE TABLE TEMP2 LIKE TEMP;

Method II :

In this case, we are creating a blank table by subsetting data method. As 1 is not equal to 2, it returns zero row.

create table temp3 as
select * from temp
where 1=2;

select case when null = null then 'Yes' else 'No' end as Result;

It will return NO as the above code is not right way to compare null values. The correct way would be to use 'is' keyword to compare -

select case when null is null then 'Yes' else 'No' end as Result;

9. Suppose you have a table named TEMP. You need to recode values of column Y, Swap values 2 and 3 in column Y

Table

UPDATE TEMP
SET Y= CASE WHEN Y = 2 THEN 3
WHEN Y = 3 THEN 2
ELSE Y END;

10. Identify second maximum value

select max(y) from temp
where y not in (select max(y) from temp);

 In this code, the logic is to remove the maximum value from the main table and then calculate the max value to figure out the second max value of the main table.

11. Identify second maximum value by a group

The code below first removes all the max values by a group from the main table. Later we calculated the second max value by a group.

select a.x, max(a.y) as maxy from temp a left join
(select x, max(y) as maxy from temp group by 1) b
on a.x = b. x and a.y = b.maxy
where b.x is null and b.maxy is null
group by 1;

12. Is the query below correct? If not, what's the issue?

SELECT custid, YEAR(ref_date) AS ref_year
FROM custmart
WHERE ref_year  >= 2015;

 The calculated column cannot be used in WHERE condition so we need to modify the above code like this -

SELECT custid, YEAR(ref_date) AS ref_year
FROM custmart
WHERE YEAR(ref_date)  >= 2015;

HR / Project Related Questions

1. Explain one of your project

• Start from problem definition
• Explain Data Cleaning, Exploration and Data Preparation Steps
• What technique / algorithm is used in the project?
• Financial (Dollar) value impact of the project

2. What are your strengths and weaknesses?

3. Why are you leaving the current organization?

4. Why should we hire you?