How Can I Efficiently Left-Pad VARCHAR Values in T-SQL?

Efficiently filling VARCHAR values ​​in T-SQL

Question: What is the most efficient way to left-pad a VARCHAR value to a specified length in T-SQL? Is the following approach the best:

<code class="language-sql">REPLICATE(@padchar, @len - LEN(@str)) + @str</code>

Answer:

While the above approach seems intuitive, it is not the most efficient use of SQL. Performing population operations in a database is often inefficient.

It is recommended to consider another method:

<code class="language-sql">RIGHT('XXXXXXXXXXXX'+ RTRIM(@str), @n)</code>

Here, 'XXXXXXXXXXXX' represents the string of padding characters (here 'X'), '@str' is the original VARCHAR value, and '@n' is the total length required.

This method uses the RIGHT function to extract the required number of characters from the concatenation of the padded string and the original string. However, it must be emphasized that, ideally, performing fill operations in the database should be avoided. Moving such operations to the application layer will significantly improve performance.

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