I discover this morning that one of (maybe all?) search forms don't show all good results.
I've activated the debug mode. It gave me this request :
SELECT t0.id as pid, t0.pk as pk, t0.pkb as pkb,t0.cck as cck,
t0.storage_location as loc,tt.id AS type_id, tt.alias AS type_alias
FROM `#__cck_core` AS t0
LEFT JOIN `#__content` AS t1 ON t1.id = t0.pk
LEFT JOIN `#__cck_core_types` AS tt ON tt.name = t0.cck
WHERE t1.state = 1 AND t1.access IN (1,1) AND ( t1.publish_up =
'0000-00-00 00:00:00' OR t1.publish_up <= '2013-08-29 10:05:40' ) AND
( t1.publish_down = '0000-00-00 00:00:00' OR t1.publish_down >=
'2013-08-29 10:05:40' ) AND t0.storage_location = "joomla_article" AND
t1.introtext REGEXP "(::a_la_une::).*1.*(::/a_la_une::)"
GROUP BY t0.pk
ORDER BY t1.created DESC
and 3 results O_o
When I put this request directly in PhpMyAdmin, it give me 8 results (good results).
In the search form configuration, I put "limit" to 300 and "Pagination" to "all"...
The limit is used to say "in how many record in the table SEBLOD must search", if you search in only 300 records when there is more records you will have certainly bad results. This option is to allow some SQL optimization. When you know the max number of records in a table the query is faster with a limit.