SELECT col1 LIKE CONCAT(col2,"some_key%") as pivot1 ... others columns ...
WHERE col1 LIKE CONCAT(col2,"some_key%") = 1

SELECT 1 as pivot1, ...
FROM ...
WHERE col1 LIKE CONCAT(col2,"some_key%")

select sum(username like '%x') from t_users where username like '%x' or 1=1;

select sum(1) from t_users where username like '%x' or 1=1;

select sum(username like '%z') from t_users where username like  '%z' ;

select sum(1) from t_users where username like '%z';