Manipulating Queries

GaussDB(DWS) 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 tsqueries.

• tsquery || tsquery

  Returns the OR-combination of the two given tsqueries.

• !! tsquery

  Returns the negation (NOT) of the given tsquery.

• 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:

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  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 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:

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