3 levels of SQL expertise (2024)

5 min read

Mar 20, 2023

What is the extent of your knowledge of SQL? Basic, intermediate or advanced?

Basic: simple select queries with filtering, inner and left joins, aggregation, confident use of date functions, CASE statement, UNIONs etc., then state that you can create SQL queries to a basic level.
Intermediate: CTEs and temp tables, window functions, string handling functions (like REPLACE, SUBSTRING, LEFT, RIGHT, CHARINDEX), do numeric calculations, handle NULLs (with ISNULL, COALESCE and NULLIF), CAST and CONVERT data types, use derived tables and subqueries, then make it clear that you have intermediate SQL skills.
If you can handle all the above plus strong data manipulation knowledge including PIVOT, recursion, use correlated subqueries, build ETL processes in code, create stored procs, functions and views, indexing, loops, dynamic SQL and have a good understanding of collation and optimisation, then let them know that you have advanced SQL knowledge and skills.

It’s important that you give an accurate assessment of your level.

Here are five SQL examples that demonstrate various basic SQL operations, including simple SELECT queries with filtering, INNER and LEFT JOINs, aggregation, confident use of date functions, CASE statements, and UNIONs.

Simple SELECT Query with Filtering:

Retrieve all employees from the employees table who are in the "Sales" department and have a salary greater than $50,000.

SELECT * 
FROM employees 
WHERE department = 'Sales' AND salary > 50000;

INNER JOIN:

Retrieve a list of orders and their corresponding customer names from the orders and customers tables using an INNER JOIN.

SELECT 
 o.order_id
 , c.customer_name 
FROM 
 orders o 
INNER JOIN customers c 
ON o.customer_id = c.customer_id;

LEFT JOIN:

Retrieve a list of all products and their sales quantities, including products with zero sales, from the products and sales tables using a LEFT JOIN.

SELECT 
 p.product_name, 
 COALESCE(s.quantity_sold, 0) AS sales_quantity 
FROM 
 products p 
LEFT JOIN 
 sales s 
ON p.product_id = s.product_id;

FAQs

3 levels of SQL expertise? ›

Identify your SQL level to showcase your expertise: Beginner: Basic syntax (SELECT, FROM, WHERE, ORDER BY). Intermediate: Craft complex queries with joins, subqueries, aggregates, and functions. Advanced: Optimize queries, use features like triggers and stored procedures, and work across various databases.

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What are the 3 components of SQL? ›

SQL has three main components: the Data Manipulation Language (DML), the Data Definition Language (DDL), and the Data Control Language (DCL).

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How do I describe my SQL skills? ›

One of the best ways to demonstrate your SQL skills in database development is to create a portfolio of projects that showcase your ability to design, create, and manipulate databases using SQL. You can use online platforms, such as GitHub, to host your projects and share them with potential employers or clients.

What are the three main SQL? ›

DDL DML DCL SQL sentences

There are 3 main types of commands. DDL (Data Definition Language) commands, DML (Data Manipulation Language) commands, and DCL (Data Control Language) commands.

How do you write basic SQL skills on a resume? ›

How to Write an SQL Resume

Step 1: Choose a template. ...
Step 2: Fill in your personal details. ...
Step 3: Add a resume summary. ...
Step 4: Outline your relevant skills. ...
Step 5: Add your professional experience. ...
Step 6: Add your education. ...
Step 7: Include relevant certifications and awards.

Apr 1, 2024

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What are the two categories of SQL? ›

SQL statements are divided into two major categories: data definition language (DDL) and data manipulation language (DML).

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What are the 5 components of SQL? ›

These SQL commands are mainly categorized into five categories:

DDL – Data Definition Language.
DQL – Data Query Language.
DML – Data Manipulation Language.
DCL – Data Control Language.
TCL – Transaction Control Language.

Aug 2, 2023

What is the basic structure of SQL? ›

The basic structure of an SQL query consists of three clauses: select, from, and where. The query takes as its input the relations listed in the from clause, operates on them as specified in the where and select clauses, and then produces a relation as the result.

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What are the 3 components of database? ›

The five major components of a database are hardware, software, data, procedure, and database access language.

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What are the types and components of SQL? ›

SQL commands are broadly categorized into Data Definition Language (DDL), Data Manipulation Language (DML), Data Control Language (DCL), Transaction Control Language (TCL), and Data Query Language (DQL), each serving distinct purposes. CREATE: Used to create database objects like tables, views, or indexes.

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