How to return default value from an SQL query

Lightning fast defaults with ISNULL

The ISNULL method unique to SQL Server returns the alternative value when the primary argument is NULL. For a singular value default:

-- When life gives you NULL, make it default
SELECT ISNULL((SELECT TOP 1 Column FROM Table WHERE Condition), 'Default') AS Alias;
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This quick trick comes handy when you're certain only a single row needs returning. Employing TOP 1 guarantees that criteria is met even with the absence of a unique identifier like Id.

Set the MAX for minimal hassle

Apply the MAX function to ensure that even if multiple rows satisfy the condition, only a scalar value is retrieved to enable a smooth application of defaults:

-- MAXimizing simplicity!
SELECT COALESCE(MAX(Column), 'Default') AS Alias FROM Table WHERE Condition;
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This approach trims the query by avoiding surplus subqueries or entangled conditional logic.

Keeping it clean with union ALL and NOT EXISTS

Another pattern to consider includes UNION ALL and a NOT EXISTS check:

-- Why explore complex jungles when you have a clean path?
SELECT Column FROM Table WHERE Condition
UNION ALL
SELECT 'Default' WHERE NOT EXISTS (SELECT 1 FROM Table WHERE Condition);
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This approach is straightforward, circumventing the need for IF-ELSE statements or other more tangled conditional logic.

Dealing with complex scenarios using OUTER APPLY

In intricate situations where defaults aren't merely for a single column or when you need default values from another query, use this approach:

-- OUTER APPLY: like your trusty swiss army knife
SELECT a.Column, ISNULL(b.DefaultColumn, 'Default') AS Alias
FROM TableA a
OUTER APPLY (SELECT TOP 1 DefaultColumn FROM TableB WHERE Condition) b;
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This is more streamlined than a subquery and facilitates an orderly manner for defining defaults, particularly with merged data.

Streamlining query performance

It's critical to guarantee your queries are efficient, particularly while dealing with substantial datasets. For optimization:

• Deploy SET NOCOUNT ON: It inhibits the transmission of DONE_IN_PROC messages, thereby augmenting the stored procedures' performance.
• Indexing: Proper indexing of the columns active in WHERE conditions and JOINs is vital.
• Avoiding extraneous columns: Exclude any superfluous columns in your SELECT list that aren't vital to the outcome.

As a result, you ensure rapid responses and a minimized load on the SQL server.