create table t1 (pk int primary key);
insert into t1 values (1),(2),(3),(4),(5),(6),(7),(8),(9),(10);
select * from t1 order by now(), cast(pk as char(0));
pk
1
10
2
3
4
5
6
7
8
9
show warnings;
Level	Code	Message
Warning	1292	Truncated incorrect CHAR(0) value: '1'
Warning	1292	Truncated incorrect CHAR(0) value: '2'
Warning	1292	Truncated incorrect CHAR(0) value: '3'
Warning	1292	Truncated incorrect CHAR(0) value: '4'
Warning	1292	Truncated incorrect CHAR(0) value: '5'
Warning	1292	Truncated incorrect CHAR(0) value: '6'
Warning	1292	Truncated incorrect CHAR(0) value: '7'
Warning	1292	Truncated incorrect CHAR(0) value: '8'
Warning	1292	Truncated incorrect CHAR(0) value: '9'
Warning	1292	Truncated incorrect CHAR(0) value: '10'
drop table t1;
#
# MDEV-17020: Assertion `length > 0' failed in ptr_compare upon ORDER BY with bad conversion
#
set @save_sql_mode= @@sql_mode;
SET @@sql_mode= '';
CREATE TABLE t1 (pk INT PRIMARY KEY);
INSERT INTO t1 VALUES (1),(2);
explain
SELECT * FROM t1 ORDER BY 'foo', CONVERT(pk, CHAR(0)) LIMIT 2;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	index	NULL	PRIMARY	4	NULL	2	Using index; Using filesort
SELECT * FROM t1 ORDER BY 'foo', Cast(pk as CHAR(0)) LIMIT 2;
pk
1
2
Warnings:
Warning	1292	Truncated incorrect CHAR(0) value: '1'
Warning	1292	Truncated incorrect CHAR(0) value: '2'
set @@sql_mode= @save_sql_mode;
drop table t1;