将列从nvarchar更改为int并转换数据

Question

I have a Users table that is used to hold data for a user's gender in nvarchar(6) format. I changed the software to use enums to indicate gender and thus wish to save data as an int.

0 = Male, 1 = Female.

I put each username and old nvarchar gender in a separate table and have converted the gender column in the original Users table to an int column. How can I set my query up to take all the users in my temp table and match them by user name to users in the Users table and then set the gender = 0 or 1 depending on if the old value is "Female" or "Male"?

Users
id int PK
Username nvarchar (50)
Gender int

tempTable
id int PK (Clusted Index w/no relation to the User's PK)
username nvarchar (50)
gender nvarchar (6)

I want to match users in tempTable by username to users in Users table by Username and update the Users.Gender value to either 0 or 1 based on tempTable.gender being either male or female.

Answer 1

Something like this should work:

update a set gender = case b.Gender
                                when 'Male' then 0
                                when 'Female' then 1
                          end
from users a inner join
    tempTable b on b.Username = a.Username

This assumes every 'old' value is either Male or Female, and doesn't account for bad/missing data.