6.1 — INNER JOIN Basics

What You'll Learn

• How to use INNER JOIN to combine data from multiple tables
• The Excel VLOOKUP analogy for joining tables
• Basic join syntax and examples

From Excel to SQL: VLOOKUP vs. JOIN

In Excel, you use VLOOKUP to bring in data from another sheet. In SQL, you use JOIN to combine tables based on a common column.

Example: Combine sales with product details

Table sales:

ProductID	Amount
101	120
102	80
103	50

Table products:

ProductID	ProductName
101	Apples
102	Oranges
104	Bananas

SQL:

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

• INNER JOIN returns only rows where the ProductID exists in both tables.

Note on Table Aliases

In SQL, you can assign a short alias to each table to make your queries easier to read and write. For example, sales as s means you can refer to the sales table as s in the rest of your query. Similarly, products as p lets you use p as a shortcut for the products table.

• This is especially helpful when joining multiple tables or when column names are the same in different tables.
• Use the alias when referencing columns, e.g., s.ProductID or p.ProductName.
• It helps in the SELECT clause to indicate from which table the column should be used.

Key Points

• INNER JOIN is like VLOOKUP, but more powerful and flexible.
• Always specify the join condition with ON.
• You can join on any matching columns, not just IDs, not just on one-couple of columns.

Next Steps

Next, you’ll learn how to use LEFT JOIN to include unmatched rows—just like handling missing data in Excel.