是否对使用“ OR”的SQL SERVER表达式的所有部分进行求值？ [英] Do all parts of a SQL SERVER expression using 'OR' get evaluated?

问题描述

给出：

 在哪里（@Id为NULL或@Id = Table.Id） 
  

如果@Id为null：该表达式的值为true。第二部分@Id = Table.Id是否仍然被考虑？

这是很重要的，因为某些复杂得多的OR

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更新：

此后，我发现此语法是不错的选择

 在哪里（Table.Id = ISNULL（@Id，Table.Id））
  

解决方案

有时候是，有时不是。 SQL Server不保证布尔运算符短路，请不要依赖于布尔运算符短路是否正确。请参阅此博客条目：布尔运算符短路。

依赖于此类变量的复杂查询最好写为显式IF语句：

  IF（@id IS NULL）
 SELECT ... FROM ... WHERE ... 
 ELSE 
 SELECT ... FROM ..在哪里... 
  

Given:

WHERE (@Id Is NULL OR @Id = Table.Id)

If @Id is null: the expression evaluates to true. Does the second part @Id = Table.Id still get considered? or is it sufficient that the expression evaluates to true given that the first part is (which is the case in c#).

This is relevant because of some much more complex OR statements where it is important to know if all parts are getting evaluated.

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UPDATE:

I have since found this syntax to be a good alternative

WHERE (Table.Id = ISNULL(@Id, Table.Id))

解决方案

Sometimes they are, sometimes they aren't. SQL Server does not guarantee boolean operator short circuit, don't rely on it for correctness. See this blog entry: Boolean Operator Short Circuit.

Complex queries that depend on @variables like this are much better written as explicit IF statements:

IF (@id IS NULL)
  SELECT ... FROM ... WHERE ...
ELSE
  SELECT ... FROM ... WHERE ...

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