Top 10 SQL Query Concepts for Job Interview
If you are preparing for the software developer job, here is the list of SQL concepts you must know. In interview, interviewer can ask you to describe any of the basic SQL concepts or to write SQL queries to perform certain task on the data from the database.
Basic SQL Concepts for Job Interview
- SELECT and FROM:
This is the most important SQL query which is used to retrieve or read the data from the database. This is also called as “heart” of any SQL query.
SELECT <columns> FROM <table>
This acts as a filter for the SELECT SQL command. With the WHERE condition, you can select only relevant rows.
- GROUP BY:
This is aggregator. Using it with the SELECT query you can group column data.
- AVG / SUM / MAX / MIN:
These are aggregate functions to apply on the numeric values. It helps you to summarise the data.
- COUNT and DISTINCT:
Count helps you to find the number of rows or entries. Distinct is used to find the unique entries.
To understand these basic SQL concepts practically, check the SQL commands explained with examples.
Above are the very basic and essential SQL concepts.
Now, let’s look into some of the advance SQL concepts. Whether you are a fresher or experienced candidate, you must follow these advance SQL concepts.
Advance SQL Commands/Concepts
- CASE WHEN:
This is a very useful way to create a new derived field or perform complex aggregate operations.
Join clause is used to combine the data from different tables using join conditions. Basically, there are inner, full, left and right join.
If you are preparing for interview, get familiar with inner and left/right/full outer joins.
Union and Union All is allow you to combine data from multiple tables. The tables should have similar structure.
- WINDOW FUNCTION:
This function is used to perform calculations across a set of rows.
- CTE and SUBQUERY:
With this concept, you can create more complex queries by combining smaller queries.
Also, read the difference between SQL and NoSQL databases. Now a days, NoSQL database are getting more popular.
Follow these SQL concepts for job interview. If you have any query to discuss, ask me in the comment section below.