Wednesday, February 14, 2024

SQL - Questions for some job interviews

As you are aware, the majority of competent interviewers will be more interested in your approach and problem-solving skills than in meticulously examining your syntax. 

Instead of obsessing over understanding every scenario that may occur, concentrate more on the resources in your toolkit. 

In most recent interview, we examined a schema and answered a few queries about joins, filtering, aggregations (including running totals), CTEs, and rank/windows.

The most common things, you should be needed in the SQL interview:
  • Simple things like Select Distinct, Count, Count Distinct, Min/Max, Sum.
  • Windows functions like Lag, Over, Partition by
  • Joins, using the filter clause in join to filter to one result instead of using where.
  • Group by, Order By

1. Can you explain the difference between where and having?

Answer - When it comes to the sequence in which executable operations are performed, "WHERE" is used to filter out things from the table, while "HAVING" is used in conjunction with aggregate functions like "SUM" or "AVG" to filter out certain aggregated items.

Example - Fruits Data Table




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 SQL Query -

"SELECT Fruit, Sum(Price) as Total 
FROM Fruits
WHERE Fruit = 'Banana' 
HAVING  Sum(Price) > 10.00;"
 2. Can you explain π—›π—Όπ˜„ does π—¦π—€π—Ÿ statement execute?

Answer -The SQL execution order is the sequence in which the different clauses of a SQL query are executed. This order is important because it determines how the data is filtered, grouped, and ordered.

SQL - SQL Execution Order | π—›π—Όπ˜„ π—¦π—€π—Ÿ π—€π˜‚π—²π—Ώπ—Άπ—²π˜€ 𝗔𝗿𝗲 π—˜π˜…π—²π—°π˜‚π˜π—²π—±

3. How to remove duplicate records in SQL?

Answer - Duplicates in a dataset can skew analysis results. You can remove duplicates using the DISTINCT keyword or by using the GROUP BY clause.

How to remove duplicates records in SQL

3. How to find out employees and their manager in SQL query?
Answer - To achieve this in SQL, we are using self join technique to combine rows from two or more tables based on a related column between them.

Employee and their manager sql query example

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