Why NATURAL join and its risks in PostgreSQL? - Purpose & Use Cases

The Big Idea

What if a simple automatic join silently breaks your data without you noticing?

The Scenario

Imagine you have two lists of friends from different groups, and you want to find who appears in both lists by matching their names. Doing this by hand means checking each name one by one, which takes forever and is easy to mess up.

The Problem

Manually comparing lists is slow and mistakes happen easily, like missing a name or mixing up details. When tables have many columns, it's hard to remember which ones to match, leading to wrong or incomplete results.

The Solution

The NATURAL join automatically matches columns with the same names in both tables, saving you from writing long conditions. But it can be risky because if new columns with the same name appear, it might join on them unexpectedly, causing confusing results.

Before vs After

✗ Before

SELECT * FROM table1 JOIN table2 ON table1.id = table2.id AND table1.name = table2.name;

✓ After

SELECT * FROM table1 NATURAL JOIN table2;

What It Enables

NATURAL join lets you quickly combine tables by shared columns without extra code, but you must watch out for hidden surprises when table structures change.

Real Life Example

Suppose a store has separate tables for orders and customers, both with a 'customer_id' column. Using NATURAL join can quickly show all orders with customer details, but if a new 'address' column is added to both tables, the join might include it unexpectedly, causing errors.

Key Takeaways

NATURAL join matches tables by all columns with the same names automatically.

This saves time but can cause unexpected results if tables change.

Always check your tables' columns before using NATURAL join to avoid risks.