Comparing strings

After taking a brief look at the stemming process, it is time to figure out how a stemmed text can be compared to a user query. The following code snippet checks for wanted:

test=# SELECT to_tsvector('english', 'A car, I want a car. I would not even mind having many cars') @@ to_tsquery('english', 'wanted'); 
 ?column?  
---------- 
 t 
(1 row)

Note that wanted does not actually show up in the original text. Still, PostgreSQL will return true. The reason is that want and wanted are both transformed to the same lexeme so the result is true. Practically, this makes a lot of sense. Imagine you are looking for car on Google. If you find pages selling cars, this is totally fine. Finding common lexemes is therefore an intelligent idea.

Sometimes, people are not only looking for a single word but want to find a set of words. With to_tsquery, this is possible as shown in the next example:

test=# SELECT to_tsvector('english', 'A car, I want a car. I would not even mind having many cars') @@ to_tsquery('english', 'wanted & bmw'); 
 ?column?  
---------- 
 f 
(1 row)

In this case, false is returned because bmw cannot be found in our input string. In the to_tsquery function, & means and and | means or. It is therefore easily possible to build complex search strings.