T-SQL Group by When empty ResultSet

Question

空ResultSet和part recordselect如何在group by中计数

Table T 模式是 A 列 int，B 列 int

数据演示A是

数据演示B是

数据演示C是

A    B
(empty record)

我想要 select 这个 ResultSet

A    B
1    Bcount
2    Bcount
3    Bcount
4    Bcount

我的sql代码是

select A,Count(B) FROM T
group by A

当数据演示A时我输了A=4结果

当数据演示B我输了A=1结果

当数据演示 C 丢失所有结果时，ResultSet 为空。

Answer 1

这个问题还不清楚，但也许你在找

select v.A, count(t.b)
from (select 1 as A union select 2 union select 3 union select 4) as v 
left join t on t.a = v.a 
group by 1

Answer 2

您可以左联接到 VALUES

SELECT V.A, COUNT(T.B) AS Total_B
FROM (VALUES (1),(2),(3),(4)) V(A)
LEFT JOIN T ON (T.A = V.A) 
GROUP BY V.A
ORDER BY V.A;

或者为 A 的值创建一个引用 table。然后左连接到引用table.

CREATE TABLE REF_A (A INT PRIMARY KEY);
INSERT INTO REF_A (A) VALUES (1),(2),(3),(4);

SELECT A.A, COUNT(T.B) AS Total_B
FROM REF_A A
LEFT JOIN T ON (T.A = A.A) 
GROUP BY A.A
ORDER BY A.A;

演示 db<>fiddle here

T-SQL Group by When empty ResultSet

T-SQL Group by When empty ResultSet

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