Parsing Queries

MogDB provides functions to_tsquery and plainto_tsquery for converting a query to the tsquery data type. to_tsquery offers access to more features than plainto_tsquery, but is less forgiving about its input.

to_tsquery([ config regconfig, ] querytext text) returns tsquery

to_tsquery creates a tsquery value from querytext, which must consist of single tokens separated by the Boolean operators & (AND), | (OR), and ! (NOT). These operators can be grouped using parentheses. In other words, the input to to_tsquery must follow the general rules for tsquery input, as described in Text Search Types. The difference is that while basic tsquery input takes the tokens at face value, to_tsquery normalizes each token to a lexeme using the specified or default configuration, and discards any tokens that are stop words according to the configuration. Example:

mogdb=# SELECT to_tsquery('english', 'The & Fat & Rats');
   to_tsquery
---------------
 'fat' & 'rat'
(1 row)

As in basic tsquery input, weight(s) can be attached to each lexeme to restrict it to match only tsvector lexemes of those weight(s). Example:

mogdb=# SELECT to_tsquery('english', 'Fat | Rats:AB');
    to_tsquery
------------------
 'fat' | 'rat':AB
(1 row)

Also, the asterisk (*) can be attached to a lexeme to specify prefix matching:

mogdb=# SELECT to_tsquery('supern:*A & star:A*B');
        to_tsquery
--------------------------
 'supern':*A & 'star':*AB
(1 row)

Such a lexeme will match any word having the specified string and weight in a tsquery.

plainto_tsquery([ config regconfig, ] querytext text) returns tsquery

plainto_tsquery transforms unformatted text querytext to tsquery. The text is parsed and normalized much as for to_tsvector, and then the & (AND) Boolean operator is inserted between surviving words.

For example:

mogdb=# SELECT plainto_tsquery('english', 'The Fat Rats');
 plainto_tsquery
-----------------
 'fat' & 'rat'
(1 row)

Note that plainto_tsquery cannot recognize Boolean operators, weight labels, or prefix-match labels in its input:

mogdb=# SELECT plainto_tsquery('english', 'The Fat & Rats:C');
   plainto_tsquery
---------------------
 'fat' & 'rat' & 'c'
(1 row)

Here, all the input punctuation was discarded as being space symbols.