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 
select uncompressed_length(compress(@test_compress_string))=length(@test_compress_string);
uncompressed_length(compress(@test_compress_string))=length(@test_compress_string)
1
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)) type=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