填充数组交叉表中的缺失数据

Question

如何将数据汇总到数组中，才不会遗漏数据例如我要查询所有注册用户从一月到十二月的年度报告：

    with s_table as (

    SELECT
     city,
     gs.mounth as month,
     coalesce(count(city),0) as count
    FROM
     generate_series('2017-01-01'::date, '2017-12-31'::date , interval '1 month') as gs(mounth)
    LEFT JOIN "user"
        ON to_char("user".datereg, 'YYYY-MM') = to_char(gs.mounth::date, 'YYYY-MM')
    GROUP BY city, gs.mounth
)
    select city,
    array_agg(count) as count
    from s_table
    group by s_table.city
    order by s_table.city;

它 returns 缺少数据：

|City  |arr_agg|
|Dublin|{1}|               //ONLY DECEMBER IS FILLED!
|Berlin|{1,4,5,10}            //ONLY JAN,MAR,APR,OCT ARE FILLED!

期待结果

    |City  |       Count users        |
    |Dublin|{0,0,0,0,0,0,0,0,0,0,0,1} |
    |Berlin|{1,0,4,5,0,0,0,0,0,10,0,0}|

如何用'0'填充缺失的数据？

Answer 1

您需要为所有城市生成所有月份。要获取行，请考虑 cross join:

with s_table as (
      select c.city, gs.month as month,
             count(u.city) as count
      from generate_series('2017-01-01'::date, '2017-12-31'::date , interval '1 month') as gs(month) cross join
           (select distinct u.city from user u) c left join
           "user" u
           on date_trunc('month', u.datereg,) = date_trunc(gs.month::date) and
              u.city = c.city
        group by c.city, gs.month
       )
select city, array_agg(count order by month) as count
from s_table
group by s_table.city
order by s_table.city;

注意答案中的其他变化：

日期比较使用日期函数而不是字符串。
array_agg() 有一个 order by。
无需将 generate_series() 的结果转换为日期。
count() 没有 return NULL，所以 coalese() 是不必要的。

填充数组交叉表中的缺失数据

filling missing data in array crosstab

sql

arrays

postgresql

crosstab

missing-data