Joining in Snowflake

Introduction to Snowflake SQL

George Boorman

Senior Curriculum Manager, DataCamp

JOINS

  • INNER JOIN
  • OUTER JOINS
    • LEFT OUTER JOIN or LEFT JOIN
    • RIGHT OUTER JOIN or RIGHT JOIN
    • FULL OUTER JOIN or FULL JOIN
  • CROSS JOINS
  • SELF JOINS
  • NATURAL JOIN
  • LATERAL JOIN
Introduction to Snowflake SQL

Pizza dataset

Pizza database schema diagram

Introduction to Snowflake SQL

NATURAL JOIN

  • NATURAL JOIN automatically match columns and eliminate duplicated ones

Syntax:

SELECT ...
FROM <table_one> [
                     {
                       | NATURAL [ { LEFT | RIGHT | FULL } [ OUTER ] ]
                     }
                   ]
                   JOIN <table_two>
[ ... ]
Introduction to Snowflake SQL

NATURAL JOIN

Without NATURAL JOIN

SELECT * 
FROM pizzas AS p 
JOIN  pizza_type AS t 
    ON t.pizza_type_id = p.pizza_type_id

Join result without natural join

With NATURAL JOIN

SELECT *
FROM pizzas AS p 
NATURAL JOIN pizza_type AS t

  Join result with natural join

Introduction to Snowflake SQL

NATURAL JOIN

 

❌ NOT ALLOWED ❌

select *
FROM pizzas AS p 
NATURAL JOIN pizza_type AS t
    ON  t.pizza_type_id = p.pizza_type_id

Syntax Error Image

Introduction to Snowflake SQL

NATURAL JOIN

$$

✅ ALLOWED ✅

  • WHERE clause
SELECT *
FROM pizzas AS p 
NATURAL JOIN pizza_type AS t
WHERE pizza_type_id = 'bbq_ckn'
Introduction to Snowflake SQL

LATERAL JOIN

  • LATERAL JOIN: lets a subquery in FROM reference columns from preceding tables or views.

Syntax:

SELECT ...
FROM <left_hand_expression> , -- 
LATERAL 
(<right_hand_expression>)

  • left_hand_expression - Table, view, or subquery

  • right_hand_expression - Inline view or subquery

Introduction to Snowflake SQL

LATERAL JOIN with a subquery

SELECT 
    p.pizza_id, 
    lat.name, 
    lat.category 
FROM pizzas AS p,

LATERAL -- Keyword LATERAL
        ( SELECT * 
          FROM pizza_type AS t

         -- Referencing outer query column: p.pizza_type_id
          WHERE p.pizza_type_id = t.pizza_type_id

        ) AS lat
Introduction to Snowflake SQL

Why LATERAL JOIN?

SELECT 
    *
FROM orders AS o,
LATERAL (
   -- Subquery calculating total_spent
    SELECT 
        SUM(p.price * od.quantity) AS total_spent
    FROM order_details AS od
    JOIN pizzas AS p 
          ON od.pizza_id = p.pizza_id
    WHERE o.order_id = od.order_id
) AS t
ORDER BY o.order_id
Introduction to Snowflake SQL

Let's practice!

Introduction to Snowflake SQL

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