Select query efficiency and effectiveness issues

These days in a database metadata collation appeared two SQL, do when, a little confused, and then turned around to ponder a bit, two SQL as follows:

Select A.*, B.BM, B.LM
From xt_sjzlgzpz_t A
Left JOIN Xt_sjzlgzpz b
On upper (Trim (A.LM)) = Upper (Trim (B.LM))
where upper (B.BM) = Upper (' Tb_stat_ywl_report ')

And

Select A.*, C.BM, C.LM
From xt_sjzlgzpz_t A
Left JOIN (SELECT *
From Xt_sjzlgzpz b
where upper (B.BM) = Upper (' Tb_stat_ywl_report ')) c
On upper (Trim (A.LM)) = Upper (Trim (C.LM))

The main difference between the two SQL is the first join and where, the efficiency is definitely the latter high, and can really show the left join effect, and the former can not!!!

Select query efficiency and effectiveness issues