What's the Difference Between '= NULL' and 'IS NULL' in SQL Queries?

Exploring the Differences between "= null" and "IS NULL"

In the realm of database querying, it's essential to understand the distinction between the operators "= null" and "IS NULL". While they may seem similar at first glance, their usage differs subtly yet significantly.

Usage of "= null"

The operator "= null" assigns the NULL value to a particular column in an UPDATE statement. For example, the query "UPDATE TableX SET Column=NULL..." assigns the NULL value to the column specified.

Usage of "IS NULL"

The operator "IS NULL" primarily serves in comparison operations in a WHERE clause. It checks whether a particular column contains the NULL value. Unlike assigning the NULL value, the syntax "column=null" is not valid in WHERE clauses. Instead, "column IS NULL" is used to test for the presence of NULL values.

Key Distinctions

1. Assignment vs. Comparison: "= null" assigns the NULL value, while "IS NULL" compares a column to the NULL value.
2. WHERE Clause Validity: "column IS NULL" is valid for use in WHERE clauses, whereas "column=null" is not.
3. NULL's Nature: NULL represents an unknown value, not an empty or zero value. As a result, comparing NULL for equality using "= null" is not valid.

Examples

• To assign NULL to a column:

  UPDATE TableX SET Column=NULL

• To compare a column to NULL in a WHERE clause:

  SELECT * FROM TableX WHERE Column IS NULL

Additional Resources

• Wikipedia NULL (SQL)
• W3schools SQL NULL Values
• SQL Tutorial, IS NULL Operator section

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