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SetGroupBy
Prototype: function SetGroupBy ( $attribute, $func, $groupsort=“@group desc” )
Sets grouping attribute, function, and groups sorting mode; and enables grouping (as described in the section called “Grouping (clustering) search results ”).
$attribute is a string that contains group-by attribute name.
$func is a constant that chooses a function applied to the attribute value in order to compute group-by key.
$groupsort is a clause that controls how the groups will be sorted. Its syntax is similar
to that described in the section called “SPH_SORT_EXTENDED mode”.
Grouping feature is very similar in nature to GROUP BY clause from SQL. Results produces by this function call are going to be the same as produced by the following pseudo code:
SELECT ... GROUP BY $func($attribute) ORDER BY $groupsort
Note that it's $groupsort that affects the order of matches
in the final result set. Sorting mode (see the section called “SetSortMode”)
affect the ordering of matches within group, ie.
what match will be selected as the best one from the group.
So you can for instance order the groups by matches count
and select the most relevant match within each group at the same time.
Starting with version 0.9.9-rc2, aggregate functions (AVG(), MIN(), MAX(), SUM()) are supported through SetSelect() API call when using GROUP BY.
Starting with version 2.0.1-beta, grouping on string attributes is supported, with respect to current collation.
