Multi-valued attribute (MVA) declaration. Multi-value (ie. there may be more than one such attribute declared), optional. Applies to SQL source types (mysql, pgsql, mssql) only.

Plain attributes only allow to attach 1 value per each document. However, there are cases (such as tags or categories) when it is desired to attach multiple values of the same attribute and be able to apply filtering or grouping to value lists.

The declaration format is as follows (backslashes are for clarity only; everything can be declared in a single line as well):

sql_attr_multi = ATTR-TYPE ATTR-NAME 'from' SOURCE-TYPE \
	[;QUERY] \
	[;RANGE-QUERY]

where

Example:

sql_attr_multi = uint tag from query; SELECT id, tag FROM tags
sql_attr_multi = uint tag from ranged-query; \
	SELECT id, tag FROM tags WHERE id>=$start AND id<=$end; \
	SELECT MIN(id), MAX(id) FROM tags