如何使用UNION获得两个独立的选择器？

Question

遗憾的是SQL是我最弱的技能。

我尝试在UNION中使用VIEW，我可以通过一个查询从两个不同的表中获取统计信息。

SELECT COUNT(*) AS `customer_count` FROM `Customers`
UNION
SELECT COUNT(*) AS `supplier_count` FROM `Suppliers`;

^{的 [Demo table]}

但是，它只返回两行 customer_count 。无论如何，要做到这一点，它会分别返回 customer_count 和 supplier_count 吗？

Answer 1

select
(SELECT COUNT(*) FROM Customers) as customer_count,
(SELECT COUNT(*) FROM Suppliers) AS supplier_count

Answer 2

使用您的表格演示。

密钥是使用别名，因此字段名称在每个联合选择上匹配。

在这种情况下TableSource和Total

SELECT 'Customer' as TableSource, Count(City) as Total FROM Customers
UNION
SELECT 'Suppliers' as TableSource, Count(City) as Total FROM Suppliers;

Answer 3

您需要cross join才能在一行中看到彼此相邻的结果。因此，如果没有select条件，您可以join。{/ p>

select * from
(select count(*) as customer_count from Customers) x,
(select count(*) as supplier_count from Suppliers) y

Answer 4

CREATE  VIEW `vw_count` AS 
select (select count(0) from `tbl`) AS   `customer_count`,
       (select count(0) from `tbl2`) AS `supplier_count`;