如题，会log issue：WARNING: Variable lbclsig already exists on file WORK.LB4.
请教大神，是什么原因！！！
code：
proc sql noprint;
        create table lb4 as
        select a.*,b.lbclsig
        from lb3 as a left join lab_ as b
        on a.usubjid=b.usubjid and a.parcat1=b.parcat1 and a.param=b.param and a.instancename=b.instancename;
quit;