| Bug #7095 | Compress/Uncompress function support Blob type | ||
|---|---|---|---|
| Submitted: | 8 Dec 2004 5:45 | Modified: | 14 Sep 2005 9:54 |
| Reporter: | TAT LIM CHIN | Email Updates: | |
| Status: | Not a Bug | Impact on me: | |
| Category: | MySQL Server | Severity: | S3 (Non-critical) |
| Version: | 4.1.15-BK | OS: | Linux (Linux) |
| Assigned to: | Jim Winstead | CPU Architecture: | Any |
[31 Aug 2005 10:22]
Valeriy Kravchuk
Test file. Shows incorrect data type VAR_STRING (253) istead of BLOB (252)
Attachment: 7095.c (text/x-csrc), 1.29 KiB.
[31 Aug 2005 10:31]
Valeriy Kravchuk
See the attached test case. The table used is the following: mysql> desc ImageFile; +-----------+---------------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-----------+---------------------+------+-----+---------+----------------+ | ID | bigint(20) unsigned | | PRI | NULL | auto_increment | | IMAGEDATA | mediumblob | YES | | NULL | | +-----------+---------------------+------+-----+---------+----------------+ 2 rows in set (0.00 sec) According to the manual (http://dev.mysql.com/doc/mysql/en/string-functions.html): "(Use of CHAR or VARCHAR to store compressed strings is not recommended. It is better to use a BLOB column instead.)" We used it in just such a way, and, as original reporter described, will get the result as string, not as a blob, thus making it impossible to use the results of uncomression as blobs directly. The result of Uncompress(BLOB) should be of a BLOB type really.
[31 Aug 2005 10:33]
Valeriy Kravchuk
The results of test: [openxs@Fedora 4.1]$ ./7095 Client info: 4.1.15 Server info: 4.1.15 type=8 length=20 decimals=0 type=253 length=8192 decimals=31
[14 Sep 2005 9:54]
Sergei Golubchik
VAR_STRING is correct for the result of the string function. What matters is the character set. The result of the UNCOMPRESS() has 'binary' character set and BINARY flag set. It means the result is binary data, not a text.
Description: Becuase application software use report designer to generate report. If application software store data to database include blob filed type like image file, i hope can compress blob data after store in database. This method has big advantage that always take small size in database, also improve speed when using MYISAM table type. I know MySQL ver 4.1 added COMPRESS/UNCOMPRESS function, but only limit for string. I already try to compress and uncompress blob data, can be succeed. But if i try to get this blob field using report designer, cannot detect this is blob field. We can return result but IMAGEDATA filed type already change to TEXT field, not a blob field type. In this case, report designer cannot detect it is blob field, so never display image in report. I use delphi 7, MYDAC V3.1, ReportBuilder v7(report designer). Thanks. How to repeat: Create Table ImageFile ( ID BIGINT UNSIGNED NOT NULL AUTO_INCREMENT, IMAGEDATA MEDIUMBLOB, PRIMARY KEY(ID) ); /* insert some image files using compress function */ Insert Into ImageFile Values(Null, COMPRESS(/* Image Data */)); /* after insert, get data using Select */ Select ID, UNCOMPRESS(IMAGEDATA) IMAGEDATA From ImageFile;