postgre级联更新

常规写法

update t_table_copy a 
set content=(
  select content from t_table b where a.id = b.id
);

这写法，数据少了还行，数据多了，17w条数据几十分钟，呸

优化写法

update t_table_copy as p 
set content = a.content
from (
　　select x.id,x.content from t_table x
) as a where p.id = a.id;

17w条数据11s