如何將此MySQL查詢最小化爲一個？

Question

我有這三個查詢，我想盡量減少到一個。我會怎麼做呢？

$query = "SELECT COUNT(*) FROM states WHERE id = 1"; 
    $query2 = "SELECT COUNT(*) FROM cities WHERE id = 5"; 
    $query3 = "SELECT COUNT(*) FROM areas WHERE id = 3"; 

如果有人指點我一些很棒的網站或文章，可以幫助我練習和理解MySQL命令，我將不勝感激。非常感謝。

編輯：我想腳本返回結合在一個結果（變量）的行數。

Answer 1

那麼，在一個查詢做到這一點的唯一方法（我知道）是這樣的：

SELECT 
(SELECT COUNT(*) FROM states WHERE id = 1) AS state_count, 
(SELECT COUNT(*) FROM cities WHERE id = 5) AS city_count, 
(SELECT COUNT(*) FROM areas WHERE id = 3) AS area_count 

這幾乎可以被稱爲「優化」，怎麼一回事，因爲還有3次表掃描，但可以」避免這些，因爲您想在三個不同的表上使用COUNT。

編輯

如果你想總和三者的數字，那麼這就是答案：

SELECT 
(
    (SELECT COUNT(*) FROM states WHERE id = 1) 
    + (SELECT COUNT(*) FROM cities WHERE id = 5) 
    + (SELECT COUNT(*) FROM areas WHERE id = 3) 
) AS sum 

Answer 2

SELECT 'states', COUNT(*) FROM states WHERE id = 1 
UNION 
SELECT 'cities', COUNT(*) FROM cities WHERE id = 5 
UNION 
SELECT 'areas' , COUNT(*) FROM areas WHERE id = 3 

編輯：我喜歡@Silver光的回答最好，但是既然（他）想不到另一種方式去做，我想我會把這個作爲參考。