How to Use the SELECT Statement in Redshift

How do I use the SELECT statement in Amazon Redshift?

SELECT returns rows from one or more Amazon Redshift tables or views, optionally filtered, sorted, and aggregated.

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Description

What does the Redshift SELECT statement do?

The SELECT statement retrieves columns and rows from Redshift tables or views. You can return every row or filter, sort, join, aggregate, and limit the result set.

How do I choose columns?

List column names after SELECT. Use * for all columns or rename with AS. Example: SELECT id, name AS customer_name FROM Customers;

How do I filter rows?

Attach a WHERE clause.Example: SELECT * FROM Orders WHERE total_amount > 100;

How do I sort results?

Use ORDER BY with ASC or DESC. Example: SELECT * FROM Products ORDER BY price DESC;

How do I join tables?

Combine rows with JOIN. Example: SELECT c.name, o.total_amount FROM Customers c JOIN Orders o ON o.customer_id = c.id;

How do I aggregate data?

Wrap columns in aggregate functions and apply GROUP BY. Example: SELECT customer_id, SUM(total_amount) AS lifetime_value FROM Orders GROUP BY customer_id;

How do I limit the number of rows?

Add LIMIT.Example: SELECT * FROM Products LIMIT 10;

Best practices for SELECT in Redshift?

Always specify columns instead of *. Use predicate pushdown (WHERE) to minimize scanned data. Employ SORTKEY and DISTKEY alignment for joins.

Why How to Use the SELECT Statement in Redshift is important

How to Use the SELECT Statement in Redshift Example Usage


--Find each customer’s latest order total
SELECT c.id, c.name, o.order_date, o.total_amount
FROM Customers c
JOIN Orders o ON o.customer_id = c.id
WHERE o.order_date = (
    SELECT MAX(o2.order_date)
    FROM Orders o2
    WHERE o2.customer_id = c.id)
ORDER BY o.total_amount DESC;

How to Use the SELECT Statement in Redshift Syntax


SELECT [DISTINCT] column_list
FROM table_expression
[WHERE condition]
[GROUP BY group_cols]
[HAVING group_condition]
[QUALIFY window_condition]
[ORDER BY sort_cols [ASC|DESC]]
[LIMIT n]

--Ecommerce sample
SELECT DISTINCT p.id, p.name, p.price
FROM Products p
JOIN OrderItems oi ON oi.product_id = p.id
WHERE p.stock > 0
ORDER BY p.price DESC
LIMIT 20;

Common Mistakes

Using SELECT * in large tables. This scans unnecessary columns, increasing query cost and slowing performance. Fix by listing only required columns.
Forgetting a WHERE clause when joining, leading to Cartesian products. Always provide join predicates in ON or USING to avoid huge result sets.