在 SQL 语句中使用 WHERE 1=1 的目的是什么? [英] What is the purpose of using WHERE 1=1 in SQL statements?
问题描述
可能的重复:
为什么一个sql查询会有“where 1 = 1”
为什么有人会使用 WHERE 1=1AND <条件>在 SQL 子句中?
我在不同的查询示例中看到了很多，它可能适用于所有 SQL 引擎.
I've seen that a lot in different query examples and it goes to probably all SQL engines.
如果有一个没有定义条件的查询，人们(尤其是 ORM 框架)通常会添加始终为真条件 WHERE 1 = 1 或类似的东西.
If there is a query that has no conditions defined people (and specially ORM frameworks) often add always-true condition WHERE 1 = 1 or something like that.
所以不是
SELECT id, name FROM users;
他们使用
SELECT id, name FROM users WHERE 1 = 1;
如果您动态添加条件，我能想到的唯一可能原因是您不必担心剥离初始 AND 但仍然经常出现此 1 = 1 如果查询中有实际条件，则条件被剥离.
The only possible reason I could think of if you are adding conditions dynamically you don't have to worry about stripping the initial AND but still quite often this 1 = 1 condition is stripped if there is an actual condition in the query.
来自 CakePHP 的实际示例(由框架生成):
Actual example from CakePHP (generated by framework):
(无条件)
SELECT `User`.`id`, `User`.`login`
FROM `users` AS `User` WHERE 1 = 1
ORDER BY `User`.`id` ASC;
(有条件)
SELECT `User`.`id`, `User`.`login`
FROM `users` AS `User`
WHERE `User`.`login` = 'me@example.com'
LIMIT 1;
有什么理由添加这个额外的条件吗?
Is there any reason for adding that extra condition?
推荐答案
是的，通常是因为它以 'where 1 = 0' 开头，从而强制语句失败.
Yeah, it's typically because it starts out as 'where 1 = 0', to force the statement to fail.
这是一种更天真的方式，将其包装在事务中而不是在最后提交，以测试您的查询.(这是首选方法).
It's a more naive way of wrapping it up in a transaction and not committing it at the end, to test your query. (This is the preferred method).
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