Queries that contain multiple etx_contains() operators

This affects how complex queries must be written. For example, suppose you are interested in finding recipes that mention lemon zest or ingredients that include orange rind. Two separate etx_contains() operators must be used in the query. Unfortunately, the following type of query returns an error because the database server cannot use a single index scan for the two etx_contains() operators:

SELECT id FROM recipes 
    WHERE etx_contains(recipe, Row ('lemon zest', 'SEARCH_TYPE = PHRASE_EXACT'))
    OR
          etx_contains(ingredients, Row ('orange rind', 'SEARCH_TYPE = PHRASE_EXACT'));

The query must be rewritten into two separate queries combined with the UNION operator, as shown in the following example:

SELECT id FROM recipes 
    WHERE etx_contains(recipe, Row ('lemon zest', 'SEARCH_TYPE = PHRASE_EXACT'))
UNION
SELECT id FROM recipes 
    WHERE etx_contains(ingredients, Row ('orange rind', 'SEARCH_TYPE = PHRASE_EXACT'));

Similarly, an AND clause involving two etx_contains() operators returns an error. The alternative is to rewrite the query as shown by the following example:

SELECT id FROM recipes 
    WHERE etx_contains(recipe, Row ('lemon zest', 'SEARCH_TYPE = PHRASE_EXACT'))
AND id IN
 (SELECT id FROM recipes 
    WHERE etx_contains(ingredients, Row ('orange rind', 'SEARCH_TYPE = PHRASE_EXACT')));