为什么这里是空的？

Question

请问有人知道这是为什么吗:

SELECT to_tsvector('an'); 

returns不过

SELECT to_tsvector('nn');

或

SELECT to_tsvector('n');

或

SELECT to_tsvector('aa');

做吗？

我正在 SUPABASE 上的 PostgreSQL 13 运行 上测试这个。

谢谢

Answer 1

因为“an”在您当前的设置中是停用词（可能是英语，默认设置）。

来自the documentation

The to_tsvector function internally calls a parser which breaks the document text into tokens and assigns a type to each token. For each token, a list of dictionaries (Section 12.6) is consulted, where the list can vary depending on the token type.

并且（强调我的）...

Some words are recognized as stop words (Section 12.6.1), which causes them to be ignored since they occur too frequently to be useful in searching.