How should I update ID field values for all records based on previous values? I need a SQL query that can update ID fields for all records in a table from their previous values to a new value based on that previous value.  

For example, if the ID is 1, I want to change it to 9991 - prepending '999' to every ID in the table.

What is the most efficient means of doing this?
A couple options come to mind.  If you have a charish data type:

update table set column=concat('999',column);


If you have an integer type find the max value, let's say it's under 10,000 then

update table set column=9990000+column