If you are a beginner, don't try to write the entire SQL query immediately. The easiest approach is to break the problem into small steps.
๐ Step 1: Understand What the Question Is Asking
Read the question carefully and identify the final output.
Example:
Find the total sales for each customer.
Ask yourself:
๐ What do I need to display?
Answer:
Customer
Total Sales
๐ Step 2: Identify the Table
Find which table contains the required information.
Suppose you have:
sales
customer_id
product
quantity
price
You need the sales table.
๐ Step 3: Identify the Required Columns
For:
Find total sales for each customer.
You need:
customer_id
quantity
price
Because: Sales = quantity ร price
๐ Step 4: Decide Whether You Need Filtering
Ask:
Do I need only certain rows?
For example:
Find total sales for customers who purchased in 2026.
Now you need a WHERE condition.
WHERE order_date >= '2026-01-01'
๐ Step 5: Decide Whether You Need GROUP BY
Look for words such as: Each customer, Each department, Per product, By region, By month
These usually indicate GROUP BY.
For example:
Find total sales for each customer.
GROUP BY customer_id
๐ Step 6: Identify the Required Aggregate Function
Look for words like:
Total โ SUM()
Average โ AVG()
Count โ COUNT()
Maximum โ MAX()
Minimum โ MIN()
For total sales:
SUM(quantity _ price)
๐ Step 7: Build the Query Step by Step
Instead of writing everything at once:
1.
SELECT customer_id FROM sales;
2.
Add the calculation:
SELECT customer_id, SUM(quantity _ price) AS total_sales FROM sales;
3.
Add grouping:
SELECT
customer_id,
SUM(quantity ** price) AS total_sales
FROM sales
GROUP BY customer_id;
Now the query is complete.
๐ Step 8: Check Whether You Need HAVING
Suppose the question changes to:
Find customers whose total sales are greater than โน50,000.
You cannot use WHERE on SUM(). Use HAVING:
SELECT
customer_id,
SUM(quantity ** price) AS total_sales
FROM sales
GROUP BY customer_id
HAVING SUM(quantity ** price) > 50000;
๐ Step 9: Check Whether You Need a JOIN
Suppose the question says:
Find the names of customers and their total sales.
You have:
customers: customer_id, customer_name
sales: customer_id, quantity, price
Now you need a JOIN.
SELECT
c.customer_name,
SUM(s.quantity ** s.price) AS total_sales
FROM customers c
JOIN sales s
ON c.customer_id = s.customer_id
GROUP BY c.customer_name;
๐ Step 10: Validate Your Answer
Before considering the problem solved, check:
โ Did I use the correct table?
โ Did I select the correct columns?
โ Is my JOIN correct?
โ Did I handle NULL values?
โ Did I accidentally create duplicates?
โ Did I use WHERE or HAVING correctly?
โ Does the output actually answer the question?
๐ง Use This SQL Problem-Solving Framework
Whenever you get a SQL question, think:
1. What is being asked?
2. Which table(s) do I need?
3. Which columns do I need?
4. Do I need filtering?
5. Do I need a JOIN?
6. Do I need aggregation?
7. Do I need GROUP BY?
8. Do I need HAVING?
9.
Do I need a window function?
10. Validate the result
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