Missng a few details, but presume you mean in sql it could be
update mytable
set [count] = [count] - 1
but that of cause is a bit odd to use a table for, because a table with just one row?
other wise there must be a key column as well to define the row in your table where there column [count] should be reduced.
if from C# instead, because of the tag on the question you could issue whatever command you want from system.data.sqlclient namespace
public static void DecrementMyTable()
{
using (var cn = new System.Data.SqlClient.SqlConnection("myconnectionstring"))
{
using (var cmd = new System.Data.SqlClient.SqlCommand("my update query"), cn)
{
md.ExecuteNonQuery();
}
}
}
You could then call a method like the outlined one on your button 'onclick' event, presuming it has runat set to 'server'