I have a table with 80,000 rows.
A column of that is username, I am going to change the table structure
since we got a user table already.

I have added a column named userID.
I would like to update the userID from user table by the username,
so far, all userID and username is unique.

How to write such query?

Update Statement
Date Range
SQL query
xp_cmdshell - works with string in one format but not in another -
How to concatenate strings from a column into a single row (with NULL value)?