= =是什麼？在H2中的意思數據庫查詢

Question

當我在看一個示例教程時，我看到了一些H2查詢，我看到這裏where =？在一些查詢中，我想知道它的含義。

查詢是

select e.id, e.summary, e.description, e.`when`, owner.id as owner_id, owner.email as 
owner_email, owner.password as owner_password, owner.first_name as owner_first_name, 
owner.last_name as owner_last_name, attendee.id as attendee_id, attendee.email as attendee_email, 
attendee.password as attendee_password, attendee.first_name as attendee_first_name, 
attendee.last_name as attendee_last_name from events as e, calendar_users as owner, 
calendar_users as attendee where e.owner = owner.id and e.attendee = attendee.id and 
(e.owner= ? or e.attendee= ?) order by e.id 

我明白大部分意味着除非它說，和（e.owner =？或e.attendee =？）

有人能簡單介紹一下最後一部分這是什麼意思？謝謝！ （：。

Answer 1

這是準備好的語句，其預計參數的標準語法

有關準備語句的詳細信息，請參見JDBC tutorial他們是一個最佳實踐遵循正確轉義特殊字符，重複使用相同的查詢了幾次都沒有每次都重新計算執行計劃，最重要的是：避免SQL injection攻擊

Answer 2

這篇Wikipedia文章解釋了標記它們用於所謂預處理語句

http://en.wikipedia.org/wiki/Prepared_statement。？。