How to set/check for a unique value in a column with CHAR (1) = y/n
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I'm not very strong in SQL statements but I would like to know about a thing I'm willing to know.

Imagine a "visible" column that holds 'y' or 'n' values. Is it possible to have <b>only</b> a single 'y' without launching a pre-query that updates this table to 'n' value for all rows before setting the desired row to 'y'?

Thanks in advance.