drop table if exists t1;
SELECT 'A' || 'B';
'A' || 'B'
AB
CREATE TABLE t1 (id INT, id2 int);
SELECT id,NULL,1,1.1,'a' FROM t1 GROUP BY id;
id	NULL	1	1.1	a
SELECT id FROM t1 GROUP BY id2;
't1.id' isn't in GROUP BY
drop table t1;