Features
IS NULL is an SQL predicate that returns TRUE when a column or expression contains the special marker NULL, indicating missing or unknown data.
IS NULL returns TRUE for columns containing NULL, allowing precise filtering of missing values. SQL treats NULL as unknown, so equality operators ( =, <> ) cannot test it; IS NULL and IS NOT NULL are required.
IS NULL is a boolean test that evaluates to TRUE when the operand contains the special NULL marker. Because NULL represents “unknown,” it is not equal to any value, including itself, so comparison operators fail. IS NULL provides a reliable way to locate missing data rows.
NULL signals the absence of any value, whereas an empty string or zero is a legitimate, known value. SQL’s three-valued logic (TRUE, FALSE, UNKNOWN) ensures arithmetic and comparisons involving NULL propagate UNKNOWN, preventing incorrect assumptions about missing data.
Use a WHERE clause with IS NULL: SELECT * FROM orders WHERE shipped_date IS NULL;. This returns only orders lacking a shipment date, highlighting items still in process.
No. = NULL always yields UNKNOWN because NULL is not comparable with equality operators. Always use IS NULL or IS NOT NULL to test for NULL values.
Use COALESCE or IFNULL: SELECT COALESCE(discount,0) AS discount FROM sales;. COALESCE returns the first non-NULL argument, turning gaps into meaningful defaults for analytics and reporting.
Audit missing foreign keys, identify incomplete forms, or monitor pipeline stages. For example, SELECT id FROM leads WHERE email IS NULL; finds records lacking critical contact data.
Galaxy’s AI copilot auto-completes IS NULL patterns, warns when = NULL appears, and suggests COALESCE usage. One-click sharing lets teams endorse the correct NULL-filter queries, eliminating Slack paste chaos.
Index selective NULL patterns only. If most rows are NULL, the index offers little benefit. Instead, create a partial index: CREATE INDEX idx_active_ship ON orders(shipped_date) WHERE shipped_date IS NULL; for efficient lookups.
Always document business meaning of NULL, prefer COALESCE in aggregations, and avoid storing placeholder strings like ‘N/A’. Validate ETL pipelines in Galaxy to ensure NULLs remain consistent after data loads.
Handling NULL correctly prevents misleading analytics. Aggregations, joins, and filters can silently drop or duplicate rows when NULL logic is misunderstood. Mastering IS NULL ensures accurate KPIs, reliable dashboards, and compliance reporting. In data engineering, explicit NULL handling avoids upstream schema drift, simplifies ETL validation, and speeds debugging in tools like Galaxy.
Performance depends on indexing and data distribution. On unindexed columns, IS NULL and `=` scans are similar. Partial indexes on NULL values can speed IS NULL filters significantly.
Use `COUNT(*) - COUNT(column_name)` or `SUM(CASE WHEN column_name IS NULL THEN 1 ELSE 0 END)`. Simple `COUNT(column_name)` ignores NULLs by design.
Yes. Galaxy highlights `= NULL` patterns, suggests IS NULL replacements, and auto-inserts COALESCE snippets to prevent NULL-related bugs.
Yes, IS NULL is ANSI-standard and behaves consistently across Postgres, MySQL, SQL Server, Snowflake, and others.
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