Richard Hipp wrote: > So if you say "group_concat(DISTINCT x,y)" does that mean that the > combination of x and y must be distinct or that only x is distinct? > Are we allowed to say "group_concat(x, DISTINCT y)" or > "group_concat(DISTINCT x, DISTINCT y)". And what does the latter > mean, exactly? > > Are there any other SQL database engines that allow multi-argument > aggregate functions? What do those systems do?
PostgreSQL says <http://www.postgresql.org/docs/9.4/static/sql-expressions.html#SYNTAX-AGGREGATES>: | aggregate_name (expression [ , ... ] [ order_by_clause ] ) | aggregate_name (ALL expression [ , ... ] [ order_by_clause ] ) | aggregate_name (DISTINCT expression [ , ... ] [ order_by_clause ] ) | | The first form of aggregate expression invokes the aggregate once for | each input row. The second form is the same as the first, since ALL is | the default. The third form invokes the aggregate once for each | distinct value of the expression (or distinct set of values, for | multiple expressions) found in the input rows. Testing <http://www.sqlfiddle.com/#!12/ddd8e/1> shows that the DISTINCT applies to the function, not to individual parameters, and that indeed the set of all parameters is checked: CREATE TABLE test ( value VARCHAR(10), delim VARCHAR(1) ); INSERT INTO test VALUES ('a', ','); INSERT INTO test VALUES ('b', ';'); INSERT INTO test VALUES ('c', '/'); INSERT INTO test VALUES ('c', '/'); INSERT INTO test VALUES ('c', ':'); INSERT INTO test VALUES ('d', ','); SELECT string_agg(DISTINCT value, delim) FROM test; => a;b:c/c,d Regards, Clemens _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
