SQL Select Where Where Clause性能問題

我有以下SQL查詢，由於where子句中的select count（1）語句而執行非常糟糕。任何人都可以提出一種方法來加速這一點嗎？這個想法是，我只希望在發現一個發票的地方返回行。SQL Select Where Where Clause性能問題

SELECT people.name, people.address 
FROM people 
WHERE ((SELECT COUNT(1) FROM invoices WHERE invoices.pid = people.id)=1)

來源

2011-04-12 Mike

COUNT(1) is superstition
你有什麼是每個人行計數爲類似行動

所以光標/循環，嘗試JOIN像這樣

SELECT people.name, people.address 
FROM 
    people 
    JOIN 
    invoices ON invoices.pid = people.id 
GROUP BY 
    people.name, people.address 
HAVING 
    COUNT(*) = 1

我還希望你有指標，至少在invoices.pid和people.pid，姓名，地址

來源

2011-04-12 04:51:47 gbn

每天學習新東西。從來沒有聽說伯爵（1）的巫術。我不知道這是否是由一些SEO人創建的... – Thomas 2011-04-12 05:08:17

謝謝！ Really Box 9的答案也如下，但是你對「迷信」的解釋和其他信息也有所幫助。 – Mike 2011-04-14 04:11:41

使用JOIN：

SELECT people.name, people.address 
FROM people 
JOIN invoices ON invoices.pid = people.id 
GROUP BY people.name, people.address 
HAVING Count(*) = 1

來源

2011-04-12 04:50:41

連接表大概是要在實踐中，性能更好，我應該認爲。

SELECT people.name, people.address 
FROM people INNER JOIN invoices ON invoices.pid = people.id

由於OP被編輯而導致編輯：您是否只希望那些只有一張發票的人？如果是這樣，那麼忽視這一點，並看看其他答案之一。

來源

2011-04-12 04:55:02 Coxy

SQL Select Where Where Clause性能問題

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