如何獲得記錄計數的總和（來自先前的查詢）

Question

我對相對複雜的SQL相當陌生，可以對問題使用一些幫助。我有一個查詢：

select 
    case 
    when group_id = 'ABC Acme' then 'ABC' 
    when group_id like 'Premium%' then 'PREM' 
    when group_id like '%Marvel%' then 'MRV' 
    else NULL 
    end client, 
    load_date, report_date, count(*) as record_count 
from tablename 
group by client, load_date, report_date 
order by client, load_date; 

返回以下內容：

client load_date report_date record_count 
ABC  4/1/2016 2/28/2016 16108 
PREM 4/19/2016 3/31/2017 5348 
MRV  4/19/2016 3/31/2017 8335 

我想，如果可能的話，得到的總和record_count（或29791）的。理想情況下，在上面的結果中添加另一行將會很好。我嘗試以下查詢，但沒有奏效...

select 
    case 
    when group_id = 'ABC Studios' then 'ABC' 
    when group_id like 'Premium%' then 'PREM' 
    when group_id like '%Marvel%' then 'MRV' 
    else NULL 
    end client, 
    load_date, report_date, count (*) 
from tablename 
    group by client, load_date, report_date 
    union all 
select 'SUM', count(*) 
from tablename; 

我得到以下錯誤：

An error occurred when executing the SQL command: 
--get summary ttl of counts by load_date for each client 
select 
case wh... 
[Amazon](500310) Invalid operation: each UNION query must have the same number of columns; 
Execution time: 0s 
1 statement failed. 

Answer 1

大多數數據庫支持grouping sets或rollup，這絕對簡化了這一點。

可維護性和一致性，我更喜歡使用一個CTE：

with t as (
     select (case when group_id = 'ABC Acme' then 'ABC' 
        when group_id like 'Premium%' then 'PREM' 
        when group_id like '%Marvel%' then 'MRV' 
       end) as client, 
      load_date, report_date, count(*) as record_count 
     from tablename 
     group by client, load_date, report_date 
    ) 
select client, load_date, report_date, record_count 
from ((select t.*, 1 as priority 
     from t 
    ) union all 
     (select 'SUM', NULL, NULL, sum(record_count), 2 
     from t 
    ) 
    ) t 
order by priority, client, load_date; 

注：

• 通過將在CTE任何潛在的過濾條件或計算，可以確保一致性。
• 實際上，數據庫按順序返回UNION ALL的行。但這並不能保證。明確使用priority列可確保數據的順序正確。
• 添加附加子集相當容易。
• grouping sets是非常優選的。

Answer 2

當你union記錄集在一起，他們需要有相同的列數。現在，您的第一個查詢有4列，第二個查詢只有2列。只需在load_date中選擇null，然後在第二個查詢中選擇report_date（無論如何，這些字段對於總計都沒有意義）。

select 
    case 
    when group_id = 'ABC Studios' then 'ABC' 
    when group_id like 'Premium%' then 'PREM' 
    when group_id like '%Marvel%' then 'MRV' 
    else 
    NULL 
    end client, load_date, report_date, count (*), 1 priority 
    from tablename 
    group by client, load_date, report_date 

    union all 

    select 'SUM', null, null, count(*), 2 priority 
    from tablename 
    order by priority; 

Answer 3

可以作爲

declare @ttl int; 
Set @ttl = (Select Count(*) from tablename) 
select 
    case 
    when group_id = 'ABC Studios' then 'ABC' 
    when group_id like 'Premium%' then 'PREM' 
    when group_id like '%Marvel%' then 'MRV' 
    else 
    NULL 
    end client, load_date, report_date, count (*), @ttl AS Sum 
    from tablename 
    group by client, load_date, report_date