Most efficient T-SQL way to pad a varchar on the left to a certain length?

Trimming the fat (i.e., spaces)

Before you begin padding, you might want to get rid of any extra spaces that could be trailing your data. This way, you can ensure your varchar length remains consistent. For such a purpose, we can utilize RTRIM:

-- "If you love your data, set it free (of spaces)."
SELECT RIGHT(REPLICATE('0', 10) + RTRIM(YourColumn), 10) AS PaddedColumn
FROM YourTable;
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By trimming the trailing spaces, we make sure that the padding operation will result in a string of the exact length we desire.

The way of the CHAR

Instead of padding your string every time you query it, you could refactor your database to use a fixed-length data type like CHAR(n). This way, you can achieve a fixed width without resorting to padding:

-- "The only thing constant is my column length!"
ALTER TABLE YourTable ALTER COLUMN YourColumn CHAR(10);
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This command changes the data type of YourColumn to CHAR(10), giving you a fixed-width string without the need to pad. Just remember that this might use excess storage if your strings are usually much shorter than 10 characters.

Optimizing performance for padding

Remember that padding operations can sometimes hog your resources and slow down performance. You must evaluate the impact of padding on the speed of your queries, especially if your database is quite large:

-- "If it's not fast, it won't last!"
SELECT ... -- Consider the impact of padding here.
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Serving efficiency and accuracy

In the world of programming, it is paramount to maintain a balance between function efficiency and the accuracy of the results you are fetching. Padding functions, while useful, can hurt performance if overused. However, you must still ensure that your data is precisely formatted:

-- "Juggle well, or you might drop the ball(s)!"
SELECT ... -- Balance efficiency and accuracy when padding.
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Dodging pitfalls with padding

You never want to add padding operations where they aren't necessary. Also, avoid incorporating them in performance-critical paths of your application, as they can be quite expensive:

-- "Padding in moderation is a good rule of thumb. Unless you're a thumb wrestler."
SELECT ... -- Minimize inefficient padding operations.
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You could also consider padding at the application level whenever feasible to offload some work from your server.

Be an efficiency guru

Here are some handy tips that could come useful while working with.padded strings:

Understand your data

Be cautious before padding zeros to the left of your string. Such varchar might erroneously be perceived as numeric values.

Maintain data integrity during exports

While importing or exporting data, ensure left-padding stays intact to avoid discrepancies across systems.

Maintain readability

Keep your code clean and understandable by enclosing padding logic within stored procedures or user-defined functions. This way, you'll avoid repetition and improve readability.