Mysql Query with field name and custom value to compare

[Rohit Seth]

We have a users table with Username and extra1 fields.
We want to pass a custom value like
$customvalue=123456;
and added to a field extra1 whose value can be anything like
extra1 = abc123
and compare its sha1 output with a seperate variable.

We tried this query but it is not working, it is not fetching the value of extra1 field so not been able to get used properly.

select Username,extra1 from users where sha1(extra1.$customvalue)='$hash'