Default to the Rescue: Filling the Gap When Your SQL Queries Come Up Empty

Using COALESCE and a Subquery:

This approach uses the COALESCE function to check if a subquery returns any rows. If not, it returns a pre-defined default row.

Example:

SELECT
    CustomerID,
    (SELECT TOP 1 'No customer found' FROM YourTable WHERE 1 = 0) AS CustomerName,
    (SELECT TOP 1 'N/A' FROM YourTable WHERE 1 = 0) AS ContactEmail
FROM YourTable
WHERE CustomerID = 123; -- Replace with your actual search criteria

Explanation:

• The main SELECT statement tries to fetch data from your table based on the CustomerID.
• The subquery inside the COALESCE function is intentionally set to never return any rows (WHERE 1 = 0).
• If the main query finds a match, the actual values from the table are used for CustomerName and ContactEmail.
• If no match is found, COALESCE returns the default values ('No customer found' and 'N/A') defined in the subquery.

Using UNION ALL with a Default Row:

This approach combines the results of your main query with a single-row table containing your default values.

SELECT
    CustomerID,
    CustomerName,
    ContactEmail
FROM YourTable
WHERE CustomerID = 123  -- Replace with your actual search criteria

UNION ALL

SELECT
    0 AS CustomerID, -- You can set any ID for the default row
    'No customer found' AS CustomerName,
    'N/A' AS ContactEmail
WHERE 1 = 0;  -- This condition ensures the default row is always included

• The main SELECT statement attempts to retrieve data from your table.
• The UNION ALL combines the results of the main query with a second query that always returns a single row with your defined default values.
• The WHERE 1 = 0 condition in the second query ensures it always returns a row, even if the main query finds no matches.

Related Issues and Solutions:

• Default Values vs. NULL: If your default row contains only NULL values, consider using ISNULL instead of COALESCE for better performance.
• Complex Default Rows: If your default row needs calculations or data from other tables, consider using a Common Table Expression (CTE) for better readability and maintainability.