What is this operator <=> in MySQL?

Digging into semantics

The <=> operator serves as a lifesaver to deal with the three-valued logic utilized by SQL: true, false, and unknown. Traditional equality operator, =, typically returns UNKNOWN with NULL comparisons, but <=> always hands out a definite outcome of 1 or 0, signifying true or false respectively.

Leveraging NULL-safe comparisons

During the creation of conditional queries, particularly within join constraints or where clauses, the <=> operator proves supremely valuable. Any column capable of housing NULL values can utilize this operator to prevent the unintentional filtering of rows containing NULL values.

SELECT *
FROM table1 T1
JOIN table2 T2 ON T1.nullable_column <=> T2.nullable_column; -- Party with NULL-values allowed 🥳


Negating NULL-safe comparisons

To reverse a NULL-safe comparison, pair the NOT operator along with <=>:

SELECT *
FROM your_table
WHERE NOT (your_column <=> NULL); -- Hide and Seek Champion: NULL 🏆


This would yield all rows where your_column is not NULL.

Trap holes and pitfalls

Here's a gotcha! It's a common mistake to believe <=> acts identically as = when NULLs are not involved. This may be accurate most times but <=> is specifically engineered for NULL-safe comparisons, so using it as a universal substitute for = might lead to unexpected outcomes.

Broader SQL dialect perspective

MySQL's <=> is often juxtaposed with SQL:2003's IS NOT DISTINCT FROM, due to their similar functionalities. When crafting cross-platform SQL code, consider alternate expressions for those DBMSs unsupported by <=>.

Applying <=> in your SQL toolbox

<=> comes in handy in data synchronization protocols and complex SQL queries that encompass subqueries with potential NULL values. Its consistent comparison outcome, regardless of the NULL status, makes it a linchpin of data integrity check tools.

Blend in with scripting languages

Where languages like PHP or Python interface with MySQL, <=> can be a handy tool to streamline NULL value management in prepared statements, bypassing the dependency on intricate conditional logic to validate NULL.

Offer for the optimizer

Utilizing <=> contributes to better query optimization in MySQL by eluding the complexities of three-valued logic which could bamboozle optimizers. This ensures a streamlined performance when dealing with NULL values.