select @test_compress_string:='string for test compress function aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa ';
@test_compress_string:='string for test compress function aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa '
string for test compress function aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa 
select length(@test_compress_string);
length(@test_compress_string)
117
select uncompress(compress(@test_compress_string));
uncompress(compress(@test_compress_string))
string for test compress function aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa 
explain extended select uncompress(compress(@test_compress_string));
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
Warnings:
Note	1003	select sql_no_cache uncompress(compress((@test_compress_string))) AS `uncompress(compress(@test_compress_string))`
select uncompressed_length(compress(@test_compress_string))=length(@test_compress_string);
uncompressed_length(compress(@test_compress_string))=length(@test_compress_string)
1
explain extended select uncompressed_length(compress(@test_compress_string))=length(@test_compress_string);
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used
Warnings:
Note	1003	select sql_no_cache (uncompressed_length(compress((@test_compress_string))) = length((@test_compress_string))) AS `uncompressed_length(compress(@test_compress_string))=length(@test_compress_string)`
select uncompressed_length(compress(@test_compress_string));
uncompressed_length(compress(@test_compress_string))
117
select length(compress(@test_compress_string))<length(@test_compress_string);
length(compress(@test_compress_string))<length(@test_compress_string)
1
create table t1 (a text, b char(255), c char(4)) engine=myisam;
insert into t1 (a,b,c) values (compress(@test_compress_string),compress(@test_compress_string),'d ');
select uncompress(a) from t1;
uncompress(a)
string for test compress function aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa 
select uncompress(b) from t1;
uncompress(b)
string for test compress function aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa 
select concat('|',c,'|') from t1;
concat('|',c,'|')
|d|
drop table t1;
select compress("");
compress("")

select uncompress("");
uncompress("")

select uncompress(compress(""));
uncompress(compress(""))

select uncompressed_length("");
uncompressed_length("")
0
create table t1 (a text);
insert t1 values (compress(null)), ('A\0\0\0BBBBBBBB'), (compress(space(50000))), (space(50000));
select length(a) from t1;
length(a)
NULL
12
76
50000
select length(uncompress(a)) from t1;
length(uncompress(a))
NULL
NULL
50000
NULL
Warnings:
Error	1259	ZLIB: Input data corrupted
Error	1256	Uncompressed data size too large; the maximum size is 1048576 (probably, length of uncompressed data was corrupted)
drop table t1;
set @@max_allowed_packet=1048576*100;
select compress(repeat('aaaaaaaaaa', IF(XXX, 10, 10000000))) is null;
compress(repeat('aaaaaaaaaa', IF(XXX, 10, 10000000))) is null
0
