关于PostgrepSQL

SET search_path TO schema [, schema, ...]

2：实现merge into

with  upd as (
   update sss.user_login  
     set download_channel='xiaomi'
     where uid = 75
returning *
)
  insert into xxxx

3: coalesce(null,1) 类似oracle中的nvl 函数

4. select regexp_split_to_table ('a,bc,d',',') 分隔

5. array_to_string(array_agg(id),',') 字符串拼接（8.4）