在NZSQL中使用limit with union all时出错

Question

我正在尝试随机抽样一周内的条目。为了确保工作日和周末条目的平衡，我绘制了两个单独的sql语句，如下所示：

select * FROM admin.acct_activity
where RANDOM() <=1
        --weekday
        and extract(day from page_hit_ts) Between 6 and 10
limit 500
UNION all

SELECT *
FROM admin.acct_activity
where RANDOM() <=1
        --weekend
        and extract(day from page_hit_ts) Between 11 and 12
limit 200
/* to-do
 1. limit results for each query
 2. order query results by date*/

错误消息为：

"all" (at char 121) expecting a keyword (State:42000, Native Code: 1B)

这是Netezza SQL (NZSQL)

第一个select语句中的limit语句似乎导致了错误。有什么建议吗？

Answer 1

我认为你可以用括号做到这一点：

(select *
 FROM admin.acct_activity
 where RANDOM() <=1 and extract(day from page_hit_ts) Between 6 and 10
 limit 500
)
UNION all
(SELECT *
 FROM admin.acct_activity
 where RANDOM() <=1 and extract(day from page_hit_ts) Between 11 and 12
 limit 200
)

如果没有，您绝对可以使用子查询来实现：

select t.*
from ((select *
       FROM admin.acct_activity
       where RANDOM() <=1 and extract(day from page_hit_ts) Between 6 and 10
       limit 500
      )
     UNION all
     (SELECT *
      FROM admin.acct_activity
      where RANDOM() <=1 and extract(day from page_hit_ts) Between 11 and 12
      limit 200
     )
    ) t

Answer 2

每个查询只能设置一条LIMIT语句。您应该将每个有限的查询放入一个临时表中，然后对临时表执行UNION ALL操作。