sql - 如何检查多个表是否具有给定 ID 的行

Question

我有几个详细信息表的主表。我需要检查每个详细信息表是否有给定 ID 的任何行。现在我正在浏览所有表格并检查 count > 0 但必须有更好的方法。

SELECT COUNT(*) FROM Table1 WHERE ID=3;
SELECT COUNT(*) FROM Table2 WHERE ID=3;
...
SELECT COUNT(*) FROM TableN WHERE ID=3;

有没有办法在一个有效的 SQL 语句中做到这一点？

Answer 1

WITH CTE AS 
(
SELECT 'T1' AS Name, COUNT(*) AS Total FROM Table1 WHERE ID=3
UNION ALL
SELECT 'T2' AS Name, COUNT(*) AS Total  FROM Table2 WHERE ID=3
UNION ALL
...
UNION ALL
SELECT 'Tn' AS Name, COUNT(*) AS Total FROM TableN WHERE ID=3;
)
Select * from CTE where Total > 0

Answer 2

这听起来像是您的桌子设计不佳。我认为您需要合并一些表或添加一个可以查询的桥接表。

或者，如果您的结构是最佳的，并且让您的应用程序处理运行每个表，请继续查询各个表。

Answer 3

If you really want one result set you can do:

DECLARE @ID INT
SET @ID = 3

SELECT 'Table1' TableName, COUNT(*) FROM Table1 WHERE ID=@ID;
UNION
SELECT 'Table2' TableName, COUNT(*) FROM Table2 WHERE ID=@ID;
UNION
...
UNION
SELECT 'TableN' TableName, COUNT(*) FROM TableN WHERE ID=@ID;

I don't see a way to not scan all tables if that's what you're trying to avoid.