Len函数对join子句

Question

Join db_abc
On a.userid = b.userid 

我想在b中的所有用户ID中加入所有用户ID，长度为4.如何在b.userid上指定Len函数，其中userid长度仅为4个字符？这是在SQL服务器

Answer 1

SELECT *
FROM a
INNER JOIN b ON a.userid = b.userid AND LEN(b.userid) = 4

Answer 2

...
JOIN db_abc b
    ON a.userid = b.userid
        AND LEN(b.userid) = 4
...