How Does MySQL's `` Null-Safe Equal Operator Work?

MySQL's <=> Operator: A Deeper Understanding

In MySQL, the <=> operator is often encountered in queries, but its purpose can be a bit ambiguous. This article aims to clarify its meaning and explore its applications.

What is the <=> Operator?

The <=> operator in MySQL is known as the "null-safe equal" operator. It behaves similarly to the regular = operator, which compares two values and returns 0 (not equal) or 1 (equal). However, <=> handles NULL values differently.

NULL Handling

Unlike the regular = operator, <=> treats NULL values as any other value. This means that a comparison of a value to NULL will never result in NULL as the outcome. Instead, <=> returns 0 if the values are not equal and 1 if they are equal.

For example, the query:

WHERE p.name <=> NULL

will return all rows where the p.name column is either NULL or not NULL.

Usefulness of the <=> Operator

The <=> operator is particularly useful when both operands may contain NULL values and you need a consistent comparison result. Additionally, it can be used with prepared statements, where the placeholder can accept both scalar values and NULL without requiring changes to the query.

Related Operators

MySQL also provides two other operators for comparing against NULL: IS NULL and IS NOT NULL. These operators are part of the ANSI standard and are supported by other databases as well. They can be seen as specializations of the <=> operator:

• 'a' IS NULL ==> 'a' <=> NULL
• 'a' IS NOT NULL ==> NOT('a' <=> NULL)

Support

While <=> is MySQL-specific, the SQL:2003 standard introduced a similar predicate called IS [NOT] DISTINCT FROM. This predicate works identically to MySQL's <=> operator.

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