!= vs <> in T-SQL

Both != and <> are valid operators to express inequality in T-SQL. They are functionally equivalent and can be used interchangeably.

Here's a breakdown of their usage:

• !=: This is the more commonly used operator in most programming languages, including T-SQL. It stands for "not equal."
• <>: This is an alternative operator that also means "not equal." It is a legacy symbol from earlier versions of SQL and is still supported for compatibility reasons.

Example:

DECLARE @x INT = 5;
DECLARE @y INT = 10;

-- Both of these conditions evaluate to TRUE:
IF @x != @y
    PRINT 'x is not equal to y';

IF @x <> @y
    PRINT 'x is not equal to y';

Choosing between != and <> is largely a matter of personal preference or coding style. However, since != is more widely used and consistent with other programming languages, it's often considered the preferred option in T-SQL.

In summary:

• Both != and <> are valid operators for not equal comparisons in T-SQL.
• They are functionally equivalent and can be used interchangeably.
• != is generally preferred due to its wider usage and consistency with other programming languages.

Understanding != vs. <> in T-SQL with Example Code

DECLARE @x INT = 5;
DECLARE @y INT = 10;

-- Using `!=`
IF @x != @y
    PRINT 'x is not equal to y';

-- Using `<>`
IF @x <> @y
    PRINT 'x is not equal to y';

In this example:

• We declare two variables, @x and @y, and assign them different values.
• Both IF statements will execute and print the message "x is not equal to y" because the values of @x and @y are indeed different.

Another Example:

SELECT *
FROM Customers
WHERE City <> 'New York';

This query will retrieve all records from the Customers table where the city is not "New York".

Key Points:

• Functionality: Both operators perform the same comparison.
• Preference: While either operator can be used, != is often preferred due to its wider usage and consistency with other programming languages.
• Compatibility: Both operators are supported in T-SQL.

Alternative Methods for Inequality Comparisons in T-SQL

While != and <> are the primary operators used for inequality comparisons in T-SQL, there are a few alternative methods that you can consider:

Using the NOT Operator with =

You can combine the NOT operator with the equality operator (=) to achieve the same result as != or <>. For example:

IF NOT (@x = @y)
    PRINT 'x is not equal to y';

Leveraging CASE Expressions

A CASE expression can be used to conditionally evaluate expressions based on different conditions. If the condition evaluates to FALSE, the ELSE clause can be used to handle the inequality case.

CASE WHEN @x = @y THEN 'x is equal to y' 
     ELSE 'x is not equal to y' 
END;

Using EXISTS or NOT EXISTS

In certain scenarios, especially when dealing with subqueries or set operations, EXISTS or NOT EXISTS can be used to check for the existence or non-existence of a condition.

IF NOT EXISTS (SELECT 1 WHERE @x = @y)
    PRINT 'x is not equal to y';

Using IN or NOT IN

If you're comparing a value against a list of values, IN or NOT IN can be used.

IF @x NOT IN (1, 2, 3)
    PRINT 'x is not equal to 1, 2, or 3';