How to Filter Data in BigQuery

Galaxy Glossary

How do I filter rows in BigQuery using the WHERE clause?

Use the WHERE clause to return only rows that meet specified conditions, improving speed and reducing cost.

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Description

Example H2

Example H3

Why use a WHERE clause to filter data in BigQuery?

Filtering trims scanned bytes, speeds queries, and delivers just the rows you need for analysis or dashboards—ideal for cost-aware, high-volume ecommerce workloads.

What is the basic syntax?

Write SELECT columns FROM dataset.table WHERE condition. Combine conditions with AND/OR, group with parentheses, or negate with NOT.

How do I filter by exact value?

Use equality operators: WHERE name = 'Alice' or WHERE product_id = 42.

How do I filter recent records?

Compare dates/timestamps: WHERE order_date >= DATE_SUB(CURRENT_DATE(), INTERVAL 7 DAY). Works well for rolling-window revenue checks.

Can I filter within a list?

Yes, with IN: WHERE status IN ('SHIPPED','DELIVERED'). BigQuery rewrites it efficiently.

How do I filter numeric ranges?

Use BETWEEN for readability: WHERE total_amount BETWEEN 100 AND 500. Equivalent to two comparisons joined with AND.

How to handle NULLs?

Use IS NULL or IS NOT NULL. Equality operators skip NULL because three-valued logic treats comparisons as unknown.

Best practices for filtering

Qualify tables with project.dataset.table, prefer DATE/TIMESTAMP literals over strings, and cast once—avoid functions on columns inside WHERE to keep filters sargable.

What are common mistakes?

1. Comparing different data types: WHERE created_at = '2024-06-01' forces a cast and can fail. Fix by using DATE or TIMESTAMP literals.
2. Forgetting to quote strings: unquoted text is parsed as identifiers and errors out. Always quote string literals in single quotes.

Why How to Filter Data in BigQuery is important

How to Filter Data in BigQuery Example Usage


-- Customers who placed high-value orders in the last 30 days
SELECT c.id,
       c.name,
       o.total_amount
FROM   `shop.Customers`  AS c
JOIN   `shop.Orders`     AS o ON o.customer_id = c.id
WHERE  o.order_date >= DATE_SUB(CURRENT_DATE(), INTERVAL 30 DAY)
  AND  o.total_amount > 500
ORDER  BY o.total_amount DESC;

How to Filter Data in BigQuery Syntax


SELECT [column_list]
FROM `project.dataset.table`
WHERE condition1 [AND|OR] condition2 [...]

condition ::= 
    column { = | != | <> | > | < | >= | <= } expression
  | column BETWEEN expression AND expression
  | column IN (expression [, ...])
  | column LIKE pattern
  | expression IS [NOT] NULL
  | EXISTS (subquery)
  | NOT condition
  | (condition)

-- Example context
SELECT id, name, email
FROM   `shop.Customers`
WHERE  created_at >= DATE_SUB(CURRENT_DATE(), INTERVAL 30 DAY);

Common Mistakes

Using string literals for dates—BigQuery must cast each value, slowing scans. Fix: use DATE 'YYYY-MM-DD' or TIMESTAMP literals to keep filters sargable.
Filtering on a function result like WHERE EXTRACT(YEAR FROM order_date)=2024, which disables partition pruning. Fix: compute the function in SELECT and keep plain column comparisons in WHERE.

Frequently Asked Questions (FAQs)

How can I do case-insensitive text filters?

Use WHERE LOWER(name) = 'alice' or compare against COLLATE NOCASE if available. Be aware that functions on columns can prevent index usage.

How do I filter arrays?

Use UNNEST to flatten: WHERE 42 IN UNNEST(product_ids). The IN predicate checks membership efficiently.

Can I parameterize filters in BigQuery?

Yes. In scripts, declare variables (DECLARE min_date DATE) and reference them: WHERE order_date >= min_date. External tools can pass parameters via the API.