How Does MySQL's `` Operator Handle NULL Values in Comparisons?

The Elusive <=> Operator in MySQL

MySQL presents a unique operator, <=>, which can confound developers unfamiliar with its enigmatic purpose. While it bears resemblance to the conventional equal sign (=), it holds special significance in handling NULL values.

Null-Safe Comparisons

Unlike its counterpart, <=> ensures a consistent comparison outcome, regardless of NULL values' presence. Instead of yielding NULL, it interprets NULL as a specific value, enabling reliable comparisons among columns potentially containing NULLs.

Code Optimization and Prepared Statements

<=> proves particularly useful in code optimization. Take, for example, the following prepared statement:

... WHERE col_a <=> ? ...

This statement handles placeholders as either scalar values or NULL without the need for query modifications.

Alternative Operators

MySQL offers additional operators tailored for NULL comparisons:

• IS NULL: Determines if a value is explicitly NULL.
• IS NOT NULL: Verifies if a value is not NULL.

These operators act as specialized versions of <=>, expressing your intentions more clearly.

Query Transformation for Portability

To enhance portability across platforms, your query can be transformed into the following:

WHERE p.name IS NULL

Universal Support

While MySQL's <=> remains platform-specific, the SQL:2003 standard introduced a similar predicate:

IS [NOT] DISTINCT FROM 

This predicate operates identically to <=>, albeit with wider support. For universal compatibility, the following complex expression can also be employed:

CASE WHEN (a = b) or (a IS NULL AND b IS NULL)
     THEN 1
     ELSE 0
END = 1

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