pg（union all）统计总数count

在分页查询中，常用的一种做法是分两部分查询；第一部分用limit查询出需要的条数，第二步用count函数查询出总数；

sql1:  select t.id,t.create_by,t.create_date 
       from table t
       limit 0 offset 10

sql2 : select count(t.id) from talbe t

但是如果用到 union all 去查询结果集，在查询总数的时候就需要修改一下了，一般的思路是把union all 两端的数量字段统一，然后作为一个子表，执行sum（coun）就可以了；

大概是这样：

SELECT SUM	( tmpcount ) 
FROM
	(
    SELECT COUNT( t1.ID ) AS tmpcount 
    FROM	table t1 
     UNION ALL
    SELECT COUNT( t2.ID ) AS tmpcount 
    FROM w008_vedio_album t2
	) A

实际中用到的一种情境实例：

SELECT SUM
	( tmpcount ) 
FROM
	(
SELECT COUNT
	( A.ID ) AS tmpcount 
FROM
	w008_video_addr_info
	A LEFT JOIN sys_user s ON A.create_by = s.login_name
	LEFT JOIN w008_user_business_info info ON s.ID = info.sysuserid
	LEFT JOIN bpe_attach_file file ON A.ID = file.ID 
WHERE
	A.is_removed =0
	AND A.isshelves = 30 UNION ALL
SELECT COUNT
	( A.ID ) AS tmpcount 
FROM
	w008_vedio_album
	A LEFT JOIN sys_user s ON A.create_by = s.login_name
	LEFT JOIN w008_user_business_info info ON s.ID = info.sysuserid 
WHERE
	A.is_removed =0
	AND EXISTS (
SELECT
	rela.ID 
FROM
	w008_album_video_rela rela
	JOIN w008_video_addr_info addr ON rela.videoaddrinfo = addr.ID 
WHERE
	rela.vedioalbum = A.ID 
	AND addr.isshelves = 30 
	) 
	) A

结果：