Determine Oracle null == null

sql

null-handling

performance-optimization

database-queries

byNikita Barsukov·Dec 15, 2024

In Oracle, comparing NULL with NULL yields false because NULL signifies an unknown value. The correct way to compare if a value is NULL is by using IS NULL:

SELECT * FROM table 
WHERE column IS NULL; --because "unknown" is a secretive🕵️‍♂️ fellow, we need special interrogation techniques

To compare NULL as if equal to something, bring in the NVL function or IS NOT DISTINCT FROM:

SELECT * FROM table WHERE NVL(column, 'empty') = NVL(other_column, 'empty');
-- OR
SELECT * FROM table WHERE column IS NOT DISTINCT FROM other_column;
--NULL is like Schrodinger's cat🐱‍👤, it is both alive and dead until NVL opens the box

Remember, making your code efficient is as important as making it work. So always optimize and measure its performance, especially when nullable columns come into the picture.

Amp up your efficiency

Playing with nullable columns can often slow down your database queries. Keep in mind these tips to stay fast and furious🏎️!

Avoid unnecessary function calls: NVL or COALESCE might not always be the best fit. Look for alternatives that better suit your needs.
Leverage Oracle's three-valued logic: Understand how Oracle interprets NULL in expressions.
Profile, profile, profile!: dbms_utility can help you compare the performance of different approaches. Keep the need for speed⏱️ in mind.

Code clarity matters, but not at the cost of performance

Being a neat freak is alright🧹, but not at the cost of SQL query performance. Your code should not compromise speed nor be tough to decipher by your time-traveling future self🦸‍♂️.

Special attentionis needed for nulls

While dealing with null values, keep an eye out🧐 on the following:

Aggregation Tricks: Aggregate functions sidestep null values by default.
Partitioning Predicaments: Stay cautious with window functions and null mixtures.
Indexing Intricacies: Nullable columns together with function-based indexes can enhance query retrieval times.

Navigating null value pitfalls

Working with nulls can be a minefield. Here are some common traps and how to avoid them:

Confusing null with zero: Null isn't 0. So don't mix up your apples🍎 with oranges🍊.
Inequality oversights: column != value doesn't bring rows where column is null to the party.
Outer Join Jitters: When using outer joins, watch out for how nulls might gatecrash your results🕵️‍♂️.

Null handling patterns worth knowing

Navigating nulls can seem tough - but not when you have these nifty patterns🧶 up your sleeve:

Predicate Reshaping: Build queries that expressly frame comparisons, making good use of IS NULL and IS NOT NULL.
Functional Consistency: Stick to either NVL or COALESCE for easier maintenance. Like mom used to say, consistency is key🔑!
Testing galore: Test scenarios involving nulls rigorously. Better safe than sorry!