Basic NOT Usage

The NOT operator reverses the result of the condition it precedes. It changes TRUE to FALSE and FALSE to TRUE.

NOT with Other Comparison Operators

You can often replace NOT with the opposite comparison operator for clearer code.

Truth Table for NOT

The NOT operator follows this simple truth table for a condition A:

Note: NOT NULL remains NULL. The NOT operator does not convert NULL values to TRUE or FALSE.

NOT with Other Logical Operators

When combining NOT with AND or OR, you can apply De Morgan's Laws to simplify the logic.

NOT IN Operator

NOT can be combined with IN to exclude rows where a column matches any value in a list.

NOT LIKE Operator

Use NOT with LIKE to find strings that don't match a pattern.

NOT NULL Handling

Use IS NOT NULL to find non-null values in a column.

Important: Always use IS NOT NULL rather than NOT IS NULL or NOT column = NULL. The latter are incorrect syntax or will not work as expected.

Example 1: Excluding Specific Content

This example shows how to find all videos except those with specific keywords:

Example 2: Finding Incomplete User Records

This example shows how to find users with incomplete information:

Example 3: Complex Filtering with NOT

This example demonstrates how to use NOT with complex conditions:

Translation: This query finds recent videos that are NOT (popular tutorials OR popular challenges OR very popular videos).

1. Simplify When Possible

Where appropriate, use negative comparison operators (!=, <>, etc.) instead of NOT for better readability.

2. Use Parentheses for Complex NOT Expressions

When using NOT with complex expressions, use parentheses to make it clear what part of the expression is being negated.

3. Be Careful with NULL Values

Remember that NOT NULL is still NULL. Always use IS NOT NULL for checking non-null values, not NOT column IS NULL.

4. Consider Performance

Some databases may optimize queries better when written without NOT. If performance is critical, test both forms.