Manipulating Queries

openGauss provides functions and operators that can be used to manipulate queries that are already in tsquery type.

• tsquery && tsquery

  Returns the AND-combination of the two given queries.

• tsquery || tsquery

  Returns the OR-combination of the two given queries.

• !! tsquery

  Returns the negation (NOT) of the given query.

• numnode(query tsquery) returns integer

  Returns the number of nodes (lexemes plus operators) in a tsquery. This function is useful to determine if the query is meaningful (returns > 0), or contains only stop words (returns 0). For example:

  postgres=# SELECT numnode(plainto_tsquery('the any'));
  NOTICE:  text-search query contains only stop words or doesn't contain lexemes, ignored
  CONTEXT:  referenced column: numnode
   numnode 
  ---------
         0
  
  postgres=# SELECT numnode('foo & bar'::tsquery);
   numnode
  ---------
         3
  

• querytree(query tsquery) returns text

  Returns the portion of a tsquery that can be used for searching an index. This function is useful for detecting unindexable queries, for example those containing only stop words or only negated terms. For example:

  postgres=# SELECT querytree(to_tsquery('!defined'));
   querytree 
  -----------
   T
  (1 row)