drop table if exists t1;set sql_mode="MySQL40";select @@sql_mode;@@sql_modeNO_FIELD_OPTIONS,MYSQL40,HIGH_NOT_PRECEDENCEset @@sql_mode="ANSI";select @@sql_mode;@@sql_modeREAL_AS_FLOAT,PIPES_AS_CONCAT,ANSI_QUOTES,IGNORE_SPACE,ANSISELECT 'A' || 'B';'A' || 'B'ABCREATE TABLE t1 (id INT, id2 int);SELECT id,NULL,1,1.1,'a' FROM t1 GROUP BY id;id	NULL	1	1.1	aSELECT id FROM t1 GROUP BY id2;iddrop table t1;SET @@SQL_MODE="";