布尔运算符的奇怪Solr/Lucene行为 [英] Weird Solr/Lucene behaviors with boolean operators

问题描述

我正在使用Solr/Lucene查询语法中的-运算符陷入一种奇怪的行为. 如果我执行查询

I'm crashing into a weird behavior with - operators in Solr/Lucene query syntax. If I execute the query

-text AND -text 

我得到了所有预期结果(很多)，但是如果我加上一些括号，例如

I get all expected results (lot), but if I put some parenthesis like

-text AND (-text) 

或

(-text) AND (-text) 

然后我什么都没有得到.我不明白为什么. 您对此行为有解释吗?

then I get no results at all. I can't understand why. Do you have an explanation for this behavior?

谢谢.

推荐答案

在 Solr邮件列表.他们还在官方常见问题解答中添加了一个条目，内容为:

The question have been answered very well in Solr mailing list. They have also added an entry in the offical FAQ, that says:

布尔查询必须至少具有一个正"表达式(即，必须或应该)才能匹配. Solr尝试解决此问题，如果要求执行一个布尔查询，该布尔查询仅在最顶层包含否定子句 ，则会添加一个匹配所有文档的查询(即:*:*)

Boolean queries must have at least one "positive" expression (ie; MUST or SHOULD) in order to match. Solr tries to help with this, and if asked to execute a BooleanQuery that does contains only negatived clauses at the topmost level, it adds a match all docs query (ie: *:*)

如果顶级BoolenQuery在其内部包含嵌套的BooleanQuery，该嵌套的BooleanQuery仅包含否定子句，则该嵌套查询将不会被修改，并且(根据定义)它与任何文档都不匹配-如果需要，则表示外部查询将不匹配.

If the top level BoolenQuery contains somewhere inside of it a nested BooleanQuery which contains only negated clauses, that nested query will not be modified, and it (by definition) an't match any documents -- if it is required, that means the outer query will not match.

因此，只有负"值的表达式始终返回0结果，但在最高层(解析器在查询开始时静默添加*:*的最高层除外).

So expressions with only "negative" values return always 0 results, except at the topmost level, where the parser silently add a *:* at the beginning of the query.

因此，-text AND -text被转换为*:* -text AND -text，因此它具有结果，而 (-text)不会转换为(*:* -text)，因为它不在最高级别，因此(-text)没有任何结果.

Therefore -text AND -text is transformed to *:* -text AND -text and so it has results, while (-text) isn't transformed to (*:* -text), because it is not at the topmost level, and so (-text) gives no results.

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