如何使用一個查詢獲取數據庫上的總行數

Question

我有一個包含兩個表的數據庫，我想通過一個查詢獲取這些表中的行數總和。 到目前爲止牛逼嘗試：

SELECT (count(bill.*) + count(items.*)) as TTL FROM bill, items // Failed 
SELECT count(*) as TTL FROM bill, items // wrong total 
SELECT (count(bill.ID_B) + count(items.ID_I)) as TTL FROM bill, items // wrong total 
SELECT count(bill.ID_B + items.ID_I) as TTL FROM bill, items // return the biggest total 

Answer 1

使用兩個子查詢：

select (select count(1) from bill) + (select count(1) from items);