在SQL中，如何計算UNION的結果？

Question

假設我有這樣一個查詢作爲

SELECT * from frequency where (...) 
UNION 
SELECT * from frequency where (...) 

我怎麼能算多少結果從上面返回？

Answer 1

使用COUNT()功能與子查詢

SELECT COUNT(*) AS Row_Counts 
FROM 
(
    SELECT * from frequency where (...) 
    UNION 
    SELECT * from frequency where (...) 
) A 

Answer 2

爲什麼UNION？如果結合WHERE條款，你可以得到數是這樣的：

SELECT COUNT(*) 
FROM frequency 
WHERE (...) OR (...)