How to Filter Data in Redshift

How do I filter rows in Amazon Redshift using WHERE and HAVING?

Filtering in Amazon Redshift uses the WHERE clause (and related predicates) to return only rows matching specified conditions.

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Description

Example H2

Example H3

What does “filtering data” mean in Redshift?

Filtering means adding a WHERE, HAVING, or qualifier that keeps just the rows you need, cutting scan time and cost.

How do I write a basic WHERE clause?

Write SELECT column_list FROM table_name WHERE condition;. Redshift evaluates the condition for every row and returns matches.

Can I combine multiple conditions?

Use AND, OR, and parentheses to chain tests.Redshift applies them left-to-right, honoring parentheses first.

How do I filter by date ranges?

Compare timestamp columns with >=, <=, BETWEEN, or DATE_TRUNC() for period buckets.

What about NULL values?

Use IS NULL or IS NOT NULL; regular = comparisons ignore NULLs.

When should I prefer HAVING over WHERE?

HAVING filters post-aggregation, perfect for keeping only groups that meet a metric threshold, e.g., customers with total spend > $500.

How do predicates affect performance?

Narrow predicates reduce disk I/O.Place the most selective conditions first and avoid functions on indexed columns to keep zone-map pruning effective.

Best practices for clean filters?

1) Store dates in UTC
2) Normalize strings to one case
3) Avoid LIKE '%abc' patterns
4) Pre-compute heavy expressions in derived columns.

Example: Finding high-value orders in 2023

SELECT o.id, o.total_amount FROM Orders o WHERE o.order_date BETWEEN '2023-01-01' AND '2023-12-31' AND o.total_amount > 500;

Ready to go further?

Try Redshift’s DISTSTYLE KEY or sort keys on filtered columns to boost performance even more.

Why How to Filter Data in Redshift is important

How to Filter Data in Redshift Example Usage


-- Top 10 customers by spend in 2023
SELECT c.id, c.name, SUM(o.total_amount) AS total_spent
FROM Customers c
JOIN Orders o ON o.customer_id = c.id
WHERE o.order_date BETWEEN '2023-01-01' AND '2023-12-31'
GROUP BY c.id, c.name
HAVING SUM(o.total_amount) > 1000
ORDER BY total_spent DESC
LIMIT 10;

How to Filter Data in Redshift Syntax


SELECT column_list
FROM table_name
[ JOIN ... ]
WHERE condition1 [AND|OR condition2 ...]
[GROUP BY ...]
[HAVING aggregate_condition]
[ORDER BY ...]
[LIMIT n];

-- Example filters in ecommerce schema
-- 1. Customers created this year
SELECT *
FROM Customers
WHERE created_at >= DATE_TRUNC('year', CURRENT_DATE);

-- 2. Orders with total_amount > 100 AND containing out-of-stock products
SELECT o.*
FROM Orders o
JOIN OrderItems oi ON oi.order_id = o.id
JOIN Products p  ON p.id = oi.product_id
WHERE o.total_amount > 100
  AND p.stock = 0;

Common Mistakes

Using functions on filtered columns (e.g., WHERE DATE(order_date) = '2023-10-01'). Functions disable zone-map pruning. Fix by comparing raw column values: WHERE order_date >= '2023-10-01' AND order_date < '2023-10-02'.
Filtering with leading wildcards (WHERE email LIKE '%@gmail.com'), which forces full table scans. Fix by storing domain in a separate column or using search optimization with spectrum.