IS NULL vs. =NULL in SQL: What's the Difference and When Should I Use Each?

The difference between IS NULL and =NULL

In SQL, both the IS NULL and =NULL operators are used to check whether a field contains a null value. However, there are significant differences in how they operate, and improper use can lead to unexpected results.

=NULL

=NULL operator returns true only if the field is explicitly assigned a value of NULL (for example, field = NULL). However, in the WHERE clause, it treats NULL values ​​as false, thus excluding rows containing NULL values ​​from the result set.

IS NULL

IS NULL operator returns true when the field is explicitly assigned to NULL or has no value at all (for example, field IS NULL). This behavior is consistent inside and outside the WHERE clause.

When to use which operator

• Use IS NULL when you need to select rows that contain NULL values ​​or differentiate between NULL values ​​and unknown values.
• Avoid using WHERE in a =NULL clause because it excludes rows containing NULL values ​​that you might want to include in the result set. Use instead to explicitly check for NULL values. IS NULL

Example

to select all rows that contain a NULL value in the 'name' field: IS NULL

<code class="language-sql">SELECT * FROM table WHERE name IS NULL;</code>

in the WHERE clause, which incorrectly excludes rows containing NULL values: =NULL

<code class="language-sql">SELECT * FROM table WHERE name = NULL;</code>

and IS NULL, you can ensure that your SQL queries return the desired results and avoid any potential confusion or unexpected behavior. =NULL

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