How can some letter hide in SQL Server?

Question

I want to some column masking in sql column.

How can I do sql command?

Answer 1

Assuming you are using SQL Server 2008 or later, we can try using REPLICATE with SUBSTRING:

SELECT
    '**' + SUBSTRING(col, 3, 2) + REPLICATE('*', LEN(col) - 4) AS mask
FROM yourTable;

Demo

A nicer way to handle this would be to make use of regular expressions, but SQL Server does not really support a regex replace. So I offer this as an alternative.