店子查詢與重用在陳述

Question

我想存儲從一個子查詢的值的列表中陳述在我的查詢重用：

WITH ListOfIds AS (SELECT Id FROM Users) 
(SELECT COUNT(*) FROM Foo WHERE Foo.UserId IN ListOfIds) 
UNION 
(SELECT COUNT(*) FROM Bar WHERE Bar.UserId IN ListOfIds) 

它是無效的。我怎樣才能做到這一點？

Answer 1

你可以使用：

WITH ListOfIds AS (SELECT Id FROM Users) 
SELECT COUNT(*) 
FROM Foo 
WHERE Foo.UserId IN (SELECT Id FROM ListOfIds) 
UNION 
SELECT COUNT(*) 
FROM Bar 
WHERE Bar.UserId IN (SELECT Id FROM ListOfIds) 

這是一個有點毫無意義，但。

而且可能是UNION ALL而不是UNION。我沒有看到跳過計數的觀點。

---

你應該停留：

SELECT COUNT(*) 
FROM Foo 
WHERE Foo.UserId IN (SELECT Id FROM Users) 
UNION 
SELECT COUNT(*) 
FROM Bar 
WHERE Bar.UserId IN (SELECT Id FROM Users) 

我猜想，查詢優化器是足夠聰明，得到的Id列表一次。