如何更改查詢以僅顯示一行 SQL？

Question

我正在嘗試編譯每個月發生多少實例的視圖。 我有下面的代碼，它得到了我的答案，但也給出了多行。 如何將視圖限制為一行，每列是每個月的實例數量？

CREATE VIEW new_users_per_month AS 
SELECT ( 
                SELECT  COUNT(id) AS January
                FROM            master_table 
                WHERE           month(created_at)=1) AS January,                
                ( 
                SELECT  COUNT(id) AS February
                FROM            master_table 
                WHERE           month(created_at)=2) AS February,
                ( 
                SELECT  COUNT(id) AS March
                FROM            master_table 
                WHERE           month(created_at)=3) AS March
FROM master_table;

Answer 1

未正確測試，我將創建虛擬對象並稍后進行測試，但支持我的評論

select *
from
(
    select 
    t.id,
    month(t.created_at) as MTH_CRE
    from master_table as t
) as q
pivot
(
    count(id) for MTH_CRE in ([1],[2],[3],[4],[5],[6],[7],[8],[9],[10],[11],[12])
) as pvt

Answer 2

做條件聚合：

select count(case when month(created_at) = 1 then id end) as Jan,
       count(case when month(created_at) = 2 then id end) as Feb,
       count(case when month(created_at) = 3 then id end) as Mar
from master_table t;