MySQL的選擇從多個表

Question

我有這2個疑問，我想結合成一個大的查詢別名：

SELECT COUNT(*) AS ac, SUM(Views) AS vc FROM tableA 

和

SELECT COUNT(*) AS mc FROM tableB 

could'nt關於這個問題找到任何東西，它甚至有可能嗎？

Answer 1

您可以使用三個子查詢的方式做：

SELECT 
(SELECT COUNT(*) FROM tableA) AS ac, 
(SELECT SUM(Views) FROM tableA) AS vc, 
(SELECT COUNT(*) FROM tableB) AS mc 

這是不是很優雅的解決方案，但應該做你所需要的。

Answer 2

SELECT 'tableA' as tablename, COUNT(*) AS count, SUM(Views) AS sum FROM tableA 
UNION 
SELECT 'tableB' as tablename, COUNT(*) AS count, 0 AS sum FROM tableB 

Answer 3

您可以創建一個返回SELECT COUNT(*) AS mc FROM tableB的功能和使用表A

CREATE FUNCTION Func1() RETURNS INTEGER 
    BEGIN 
    DECLARE Temp INTEGER; 
    SELECT COUNT(*) INTO Temp FROM tableB; 
    RETURN IFNULL(Temp, 0); 
    END; 

    SELECT COUNT(*) AS ac, SUM(Views) AS vc, Func1() as mc FROM tableA