Views and materialized views in Snowflake - Commands & Configuration

Introduction

Sometimes you want to save a query to use it again easily or speed up repeated data lookups. Views let you save a query as a virtual table, and materialized views save the query results physically for faster access.

When you want to reuse a complex query without rewriting it every time.

When you want to simplify data access for your team by creating a named query.

When you need faster query results on data that does not change often.

When you want to save storage by not duplicating data but still have easy access.

When you want to improve performance by precomputing and storing query results.

Commands

This command creates a view named example_view that shows only active customers with their id and name. It saves the query for easy reuse.

Terminal

CREATE OR REPLACE VIEW example_view AS SELECT id, name FROM customers WHERE active = TRUE;

Expected Output

Statement executed successfully.

This command runs the saved query in example_view and shows the current active customers. Views always show fresh data from the original table.

Terminal

SELECT * FROM example_view;

Expected Output

ID | NAME

1  | Alice

3  | Carlos

5  | Emma

This command creates a materialized view named example_mat_view that stores the results of the query physically for faster access.

Terminal

CREATE OR REPLACE MATERIALIZED VIEW example_mat_view AS SELECT id, name FROM customers WHERE active = TRUE;

Expected Output

Statement executed successfully.

This command reads data from the materialized view example_mat_view. It returns faster results because data is precomputed and stored.

Terminal

SELECT * FROM example_mat_view;

Expected Output

ID | NAME

1  | Alice

3  | Carlos

5  | Emma

This command updates the materialized view to reflect any changes in the original customers table. Materialized views do not update automatically.

Terminal

ALTER MATERIALIZED VIEW example_mat_view REFRESH;

Expected Output

Statement executed successfully.

Key Concept

If you remember nothing else from this pattern, remember: views save queries for reuse and always show fresh data, while materialized views save query results for faster access but need manual refresh.

Common Mistakes

Creating a materialized view but expecting it to update automatically with data changes.

Materialized views store data physically and do not refresh automatically, so they can show outdated data.

Run ALTER MATERIALIZED VIEW ... REFRESH to update the data when needed.

Using a view when you need faster query performance on large datasets.

Views run the query every time, which can be slow on big data.

Use a materialized view to store and quickly access precomputed results.

Trying to insert or update data directly in a view or materialized view.

Views and materialized views are not tables and do not support direct data changes.

Modify the underlying base tables instead.

Summary

Create views to save and reuse queries that always show current data.

Create materialized views to store query results for faster access but refresh them manually.

Use SELECT commands on views and materialized views to get data easily.

Practice

1. What is the main difference between a view and a materialized view in Snowflake?

easy

A. A view does not store data, while a materialized view stores query results.

B. A view stores data permanently, but a materialized view does not.

C. A materialized view updates automatically with every query, but a view does not.

D. A view can only be used once, while a materialized view can be reused multiple times.

Solution

1. Step 1: Understand what a view does

   A view saves a query for reuse but does not store the actual data; it runs the query each time.

2. Step 2: Understand what a materialized view does

   A materialized view stores the results of the query physically, so it can return data faster without rerunning the query.

3. Final Answer:

   A view does not store data, while a materialized view stores query results. -> Option A

4. Quick Check:

   View = no stored data, Materialized view = stored data [OK]

Hint: Remember: views save queries, materialized views save data [OK]

Common Mistakes:

• Thinking views store data permanently
• Believing materialized views update instantly with every query
• Confusing reuse capability between views and materialized views

2. Which of the following is the correct syntax to create a materialized view in Snowflake?

easy

A. CREATE VIEW my_view MATERIALIZED AS SELECT * FROM my_table;

B. CREATE MATERIALIZED VIEW my_view AS SELECT * FROM my_table;

C. CREATE MATERIALIZED my_view VIEW AS SELECT * FROM my_table;

D. CREATE VIEW MATERIALIZED my_view AS SELECT * FROM my_table;

Solution

1. Step 1: Recall Snowflake syntax for materialized views

   The correct syntax starts with CREATE MATERIALIZED VIEW followed by the view name and query.

2. Step 2: Check each option's order and keywords

   Only CREATE MATERIALIZED VIEW my_view AS SELECT * FROM my_table; uses the correct order and keywords: CREATE MATERIALIZED VIEW my_view AS SELECT * FROM my_table;

3. Final Answer:

   CREATE MATERIALIZED VIEW my_view AS SELECT * FROM my_table; -> Option B

4. Quick Check:

   Correct syntax = CREATE MATERIALIZED VIEW [OK]

Hint: Materialized view syntax starts with CREATE MATERIALIZED VIEW [OK]

Common Mistakes:

• Mixing order of keywords
• Placing MATERIALIZED after VIEW
• Using incorrect keyword sequences

3. Given the following Snowflake SQL code:

CREATE TABLE sales (id INT, amount FLOAT);
INSERT INTO sales VALUES (1, 100.0), (2, 200.0);
CREATE MATERIALIZED VIEW sales_mv AS SELECT SUM(amount) AS total FROM sales;
INSERT INTO sales VALUES (3, 300.0);
SELECT * FROM sales_mv;

What will the SELECT query return?

medium

A. total = 600.0

B. total = 300.0 (only new rows)

C. total = 300.0 plus previous sums

D. total = 300.0

Solution

1. Step 1: Understand materialized view refresh behavior

   Materialized views in Snowflake do not automatically update after data changes; they show data as of last refresh.

2. Step 2: Analyze the timing of inserts and query

   The materialized view was created after inserting two rows (100.0 + 200.0 = 300.0). The third row (300.0) was inserted after the view creation but before the select.

3. Final Answer:

   total = 300.0 -> Option D

4. Quick Check:

   Materialized view shows data at last refresh, not latest inserts [OK]

Hint: Materialized views show data as of last refresh, not latest inserts [OK]

Common Mistakes:

• Assuming materialized views auto-update instantly
• Adding new rows to materialized view results without refresh
• Confusing materialized views with normal views

4. You created a materialized view in Snowflake but it returns outdated data after table updates. What is the best way to fix this?

medium

A. Use a normal view instead of a materialized view to get fresh data.

B. Drop and recreate the materialized view every time data changes.

C. Manually refresh the materialized view using ALTER MATERIALIZED VIEW ... REFRESH.

D. Restart the Snowflake warehouse to update the materialized view.

Solution

1. Step 1: Identify how to update materialized views

   Materialized views do not update automatically; they require manual refresh to show latest data.

2. Step 2: Choose the correct refresh method

   Snowflake supports manual refresh with ALTER MATERIALIZED VIEW ... REFRESH to update the stored data.

3. Final Answer:

   Manually refresh the materialized view using ALTER MATERIALIZED VIEW ... REFRESH. -> Option C

4. Quick Check:

   Manual refresh updates materialized view data [OK]

Hint: Use ALTER MATERIALIZED VIEW ... REFRESH to update data [OK]

Common Mistakes:

• Dropping and recreating instead of refreshing
• Restarting warehouse has no effect on view data
• Confusing materialized views with normal views for freshness

5. You want to speed up queries that aggregate large sales data but also need the most current totals. Which approach best balances speed and freshness using Snowflake views?

hard

A. Use a materialized view and schedule frequent refreshes to keep data updated.

B. Use a normal view only, since it always shows fresh data but may be slower.

C. Create a materialized view and never refresh it to save compute costs.

D. Use both a normal view and a materialized view simultaneously in the same query.

Solution

1. Step 1: Understand trade-offs between views and materialized views

   Normal views provide fresh data but can be slow on large data; materialized views are fast but need refresh to update.

2. Step 2: Find a balanced solution

   Scheduling frequent refreshes of materialized views keeps data reasonably fresh while improving query speed.

3. Final Answer:

   Use a materialized view and schedule frequent refreshes to keep data updated. -> Option A

4. Quick Check:

   Materialized view + refresh = speed + freshness balance [OK]

Hint: Schedule refreshes on materialized views for fresh and fast data [OK]

Common Mistakes:

• Not refreshing materialized views and expecting fresh data
• Using only normal views and ignoring performance
• Trying to combine views in one query without refresh strategy