drop table if exists t1,t2;
create table t1(str varchar(10) default 'def',strnull varchar(10),intg int default '10',rel double default '3.14');
insert into t1 values ('','',0,0.0);
select default(str), default(strnull), default(intg), default(rel) from t1;
default(str)	default(strnull)	default(intg)	default(rel)
def	NULL	10	3.14
explain extended select default(str), default(strnull), default(intg), default(rel) from t1;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	t1	system	NULL	NULL	NULL	NULL	1	100.00	NULL
Warnings:
Note	1003	/* select#1 */ select default('') AS `default(str)`,default('') AS `default(strnull)`,default('0') AS `default(intg)`,default('0') AS `default(rel)` from dual
select * from t1 where str <> default(str);
str	strnull	intg	rel
		0	0
explain select * from t1 where str <> default(str);
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	system	NULL	NULL	NULL	NULL	1	NULL
drop table t1;
CREATE TABLE t1 (id int(11), s varchar(20));
INSERT INTO t1 VALUES (1, 'one'), (2, 'two'), (3, 'three');
SELECT s, 32 AS mi FROM t1 GROUP BY s HAVING DEFAULT(mi) IS NULL;
ERROR HY000: Field 'mi' doesn't have a default value
DROP TABLE t1;