INSERT INTO 的第一列通过链接服务器 MS SQL -> MySQL 始终为空字符串

Question

I have a MS SQL 2005 server with a linked server connection to a MySQL 5.1.46 server, using the ODBC Connector 5.1.8 driver.

I want to, from a MS SQL job, truncate and then rebuild a remote MySQL table based on the records contained in an identically-structured local MS SQL table.

Key_ID  varchar(10)  NOT NULL  Primary
FieldA  varchar(64)
FieldB  text

Key_ID   FieldA   FieldB
======   ======   ======
ID1      A        A
ID2      B        B
ID3      C        C

The problem is, when I run the following query from MS SQL, I get an error saying "Duplicate entry '' for key 'PRIMARY'." If I remove the primary key, it will add all the records but the remote MySQL Key_ID field always returns an empty string, even though no records in the local table are NULL or empty strings.

EXECUTE ('DELETE FROM DB1.Table1') AT REMOTESERVER

INSERT INTO
 OPENQUERY( REMOTESERVER, 'SELECT * FROM DB1.Table1' )
SELECT
 Key_ID,
 FieldA,
 FieldB
FROM
 Table1

returns

Key_ID   FieldA   FieldB
======   ======   ======
         A        A
         B        B
         C        C

This makes absolutely no sense.

If I add a dummy field to the beginning of the remote MySQL table, then modify my query to insert a literal value or NULL into it, that field always comes up as an empty string and my Key_ID field returns as expected.

Dummy   varchar(64)
Key_ID  varchar(10)  NOT NULL  Primary
FieldA  varchar(64)
FieldB  text

and

EXECUTE ('DELETE FROM DB1.Table1') AT REMOTESERVER

INSERT INTO
 OPENQUERY( REMOTESERVER, 'SELECT * FROM DB1.Table1' )
SELECT
 'srsly wtf?',
 Key_ID,
 FieldA,
 FieldB
FROM
 Table1

returns

Dummy   Key_ID   FieldA   FieldB
=====   ======   ======   ======
        ID1      A        A
        ID2      B        B
        ID3      C        C

As far as I can tell, the leftmost first column is always returning an empty string. Does anybody have any possible idea why, or can give me ideas for workarounds that don't involve a dummy field that serves no purpose other than acting as a buffer field?

UPDATE: I enabled the debug logging on the ODBC driver, and found that it translates my SQL statement into:

INSERT INTO `DB1`.`Table1` (`Key_ID`, `FieldA`, `FieldB`) VALUES ( DEFAULT, 'A', 'A' )

If I add the dummy field, it runs:

INSERT INTO `DB1`.`Table1` (`Dummy`, `Key_ID`, `FieldA`, `FieldB`) VALUES ( DEFAULT, 'ID1', 'A', 'A' )

I have no idea what to think now, other than that the driver assumes that the first supplied field is always an incrementing primary key?

Answer 1

I found the answer to my own question.

The problem lies in that FieldB is a text datatype.

I changed the MySQL Table1.FieldB from text to varchar, and everything started working perfectly as expected. (Of course, I had to potentially truncate the data in my original MySQL table, but in my circumstance that isn't a huge deal.)

The baffling part is that even before I redefined the datatype, the FieldB field still INSERTed correctly, and gave no indication that its existence was the problem.

Answer 2

I just encountered the same issue and I think the problem is related with the MySQL Text type as the last column of the table.

Let's say I have the following table:

CREATE TABLE `Test` (
  `id` int(11) NOT NULL DEFAULT '0',
  `field1` int(11) DEFAULT NULL,
  `field2` varchar(16) DEFAULT NULL,
  `field3` varchar(16) DEFAULT NULL,
  `field4` varchar(1) DEFAULT NULL,
  `field5` varchar(200) DEFAULT NULL,
  `field6` text,
  `field7` text,
  `field8` text,
  `field9` text,
  `field10` text,
  `field11` text,
  `field12` text
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

And on SQL Server I execute the following (test and db.dbo.test has the same schema):

INSERT OPENQUERY (MYSQL_LINK, 'SELECT * FROM test) SELECT * FROM db.dbo.test

then id, field1 to field5 will become NULL and field6 to field 12 will have the right data.

If I do the following:

INSERT OPENQUERY (MYSQL_LINK, 'SELECT id, field1, field2, field3, field4, field5 FROM test) SELECT id, field1, field2, field3, field4, field5 FROM db.dbo.test

Then the id and field1 to field5 will have the correct data.

If I purportedly insert the the field6 too, the id will become NULL. If I insert the field7, then field2 will become NULL too and so on.

I've been using OPENQUERY to transfer dozens of MSSQL table to MySQL without any issue. After reviewing the other tables schemas I noticed that none of them ended with a TEXT type in MySQL. So I made a little change on the MySQL schema by adding an integer column at the end and voilá! It worked!

CREATE TABLE `Test_new` (
  `id` int(11) NOT NULL DEFAULT '0',
  `field1` int(11) DEFAULT NULL,
  `field2` varchar(16) DEFAULT NULL,
  `field3` varchar(16) DEFAULT NULL,
  `field4` varchar(1) DEFAULT NULL,
  `field5` varchar(200) DEFAULT NULL,
  `field6` text,
  `field7` text,
  `field8` text,
  `field9` text,
  `field10` text,
  `field11` text,
  `field12` text,
  `field13` int(11) NOT NULL DEFAULT '0',
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

And the query:

INSERT OPENQUERY (MYSQL_LINK, 'SELECT * FROM test_new') SELECT *,0 FROM db.dbo.test

I don't know where I should address this issue. Is a MSSQL OPENQUERY bug or a MySQL Connector bug? I don't know. But I hope my finding will help you guys save some time on debugging.

Answer 3

What happens if you change the

OPENQUERY( REMOTESERVER, 'SELECT * FROM DB1.Table1' ) 

Statement to

OPENQUERY( REMOTESERVER, 'SELECT Key_ID, FieldA, FieldB FROM DB1.Table1' ) 

Answer 4

INSERT INTO `DB1`.`Table1` ( `FieldB`,`Dummy`, `Key_ID`, `FieldA`) VALUES ('A', DEFAULT, 'ID1', 'A' )

如果将文本列移到顶部，则问题已解决。