Mysql – How thesqldump replaces special characters during dumping records

dumpMySQLmysqldump

i am trying to dump a particular row using java.

So that i retrieve the data by using record sets and i manually written sql script code by appending the dynamic records.

But my problem is i could not write the script for blob data fields.

Because there are some special characters are present inside blob type fields.

i need to know how mysqldump.exe is replacing special characters ?

If i know the detail means i can replace those characters as same as mysqldump process.

Best Answer

There are two ways: string and hexadecimal notation, e.g.:

'abc\' as string will be like this -> 'abc\\', all special characters are escaped
'abc\' as hexadecimal will be like this -> 0x6162635C, you can test it using HEX function - SELECT HEX('abc\\');

You can choose one of those methods. Also, try to play with --hex-blob option and check results.

Related Solutions

MySQL – How to Detect a Running mysqldump

Your only hope in this scenario is to have the PROCESS privilege.

The SUPER privilege allows you to kill processes. Naturally, you don't want that. On the other hand, the PROCESS privilege allows you to see the processlist.

According to the MySQL Documentation on the PROCESS Privilege

The PROCESS privilege pertains to display of information about the threads executing within the server (that is, information about the statements being executed by sessions). The privilege enables use of SHOW PROCESSLIST or mysqladmin processlist to see threads belonging to other accounts; you can always see your own threads.

OK, Big Deal. The PROCESS Privilege lets you see the Process List. How does that help?

You can quickly detect a mysqldump in progress when you run SHOW PROCESSLIST; and see a pattern like this in the Info field:

SELECT /*!40001 SQL_NO_CACHE */ * FROM

If you have the PROCESS Privilege and are running MySQL 5.1+, you can run this query:

select COUNT(1) mysqldumpThreads
from information_schema.processlist
where info like 'SELECT /*!40001 SQL_NO_CACHE */%';

Here is a sample output:

mysql> select COUNT(1) mysqldumpThreads
    -> from information_schema.processlist
    -> where info like 'SELECT /*!40001 SQL_NO_CACHE */%';
+------------------+
| mysqldumpThreads |
+------------------+
|                1 |
+------------------+
1 row in set (0.00 sec)

All you need to do is query for that number. If you get a nonzero, mysqldump must be running.

Give it a Try !!!

SQL Server to MySQL Migration – Remove UCS-2 Surrogate Pairs

You need to take the data from UTF-8 and convert it into UCS-2LE using something like iconv. For example, using the character in your example:

echo "010000: dcb3" | xxd -r -s -0x10000 | iconv -f "UTF-8" -t "UCS-2LE" | xxd
0000000: 3307

Now I'm not sure what character UTF-8 \xdcb3 is, but apparently it's correct translation to UCS-2LE is \U0733. If you have \0xDCB3 in the SQL Server it means it was not translated into UCS-2LE before import. You should not have surrogates in the NVARCHAR fields, UCS-2 is "surrogate agnostic". See UCS-2 vs. UTF-16 (not quite Kramer vs. Kramer).

I'm not an expert in the MySQL tool set so I can't say what step is missing that was supposed to do the iconv.

Update

to locate the records with surrogates you must turn to the binary representation, since any character function will threat the surrogates as 'special':. Luckily the string manipulation functions work on binary too with the expected semantics. Eg. CHARINDEX:

insert into test(a) values  (N'a');
insert into test(a) values  (NCHAR(0xdc83));
insert into test(a) values  (N'b');
go

select * from test where charindex(0x83dc, cast(a as varbinary(8000))) > 0;

Best Answer

Related Solutions

MySQL – How to Detect a Running mysqldump

SQL Server to MySQL Migration – Remove UCS-2 Surrogate Pairs

Related Question