使用PostgreSQL中的查询结果更新列

我在PostgreSQL 9.2中有下表,其中包含时间戳：

gid [PK](bigserial),timestamp_mes(没有时区的时间戳),time_diff(interval)

1,2012-01-23 11:03:40,空的

2,2012-01-23 11:03:42,空的

3,2012-01-23 11:03:44,空的

我添加了一个间隔列(time_diff),并希望用此查询产生的时差值填充它：

SELECT timestamp_mes - lag(timestamp_mes, 1) 
over (order by timestamp_mes) as diff
from gc_entretien.trace order by timestamp_mes

我尝试了以下查询来更新time_diff列,但没有成功：

UPDATE gc_entretien.trace set time_diff = 
(SELECT trace.timestamp_mes - lag(trace.timestamp_mes, 1) 
over (order by trace.timestamp_mes) 
from gc_entretien.trace order by timestamp_mes);

这会导致错误：

ERROR: more than one row returned by a subquery used as an expression

我应该如何使用时差查询生成的值更新time_diff列？

with new_values as (
   SELECT gid, 
          timestamp_mes - lag(timestamp_mes, 1) over (order by timestamp_mes) as diff
   from gc_entretien.trace 
)
update gc_entretien.trace as tr
  set time_diff = nv.diff
from new_values nv
where nv.gid = tr.gid;