6.2 — LEFT JOIN in Practice

What You'll Learn

• How to use LEFT JOIN to include all rows from one table, even if there's no match in the other
• How this compares to Excel's VLOOKUP with missing values
• Practical examples

Sample Tables

Table sales:

ProductID	Amount
101	120
102	80
103	50

Table products:

ProductID	ProductName
101	Apples
102	Oranges
104	Bananas

Why Use LEFT JOIN?

In Excel, if your VLOOKUP doesn’t find a match, you get #N/A. In SQL, LEFT JOIN keeps all rows from the left table and fills in NULL for missing matches.

Example: Show all sales, even if product info is missing

SELECT s.ProductID, p.ProductName, s.Amount
FROM sales s
LEFT JOIN products p
  ON s.ProductID = p.ProductID;

• All sales are shown, even if there’s no matching product in products.
• Missing product names will appear as NULL.

Filtering for Missing Matches

You can find rows with no match using WHERE:

SELECT s.ProductID, s.Amount
FROM sales s
LEFT JOIN products p
  ON s.ProductID = p.ProductID
WHERE p.ProductID IS NULL;

• This shows sales with no matching product in the products table.

Key Points

• LEFT JOIN keeps all rows from the first (left) table.
• Use it to find missing data or keep unmatched rows from the LEFT table.

Next Steps

Next, you’ll learn how to join more than two tables for advanced analysis.