MySQL 中的空 IN 子句参数列表
当您执行 IN 子句为空的 SQL 查询时会发生什么?
What happens when you do a SQL query where the IN clause is empty?
例如:
SELECT user WHERE id IN ();
MySQL 是否会按预期处理此问题(即始终为 false)，如果没有，我的应用程序在动态构建 IN 子句时如何处理这种情况?
Will MySQL handle this as expected (that is, always false), and if not, how can my application handle this case when building the IN clause dynamically?
推荐答案
如果我有一个应用程序，我正在动态构建 IN 列表，但它可能最终为空，我有时会这样做使用不可能的值初始化列表并添加到该列表中.例如.如果它是用户名列表，我将从一个空字符串开始，因为这不是一个可能的用户名.如果是 auto_increment ID，我会使用 -1 因为实际值总是正的.
If I have an application where I'm building the IN list dynamically, and it might end up empty, what I sometimes do is initialize the list with an impossible value and add to that. E.g. if it's a list of usernames, I'll start with an empty string, since that's not a possible username. If it's an auto_increment ID, I'll use -1 because the actual values are always positive.
如果这不可行，因为没有不可能的值，您必须使用条件来决定是否在 WHEREAND column IN ($values) 表达式代码>子句.
If this isn't feasible because there are no impossible values, you have to use a conditional to decide whether to include AND column IN ($values) expression in the WHERE clause.
相关文章