SELECT LAST_INSERT_ID() returns 0 after using prepared statement - c++

Question

I am using MySQL and a prepared statement to insert a BLOB record (jpeg image). After executing the prepared statement, I issue a SELECT LAST_INSERT_ID() and it returns 0.
In my code I put a breakpoint after the execution command and in a MySQL command (monitor) window, I issue the SELECT LAST_INSERT_ID() and it returns zero.
In the MySQL command (monitor) window, I issue an SQL statement to select all the IDs and the last (only) inserted ID is 1 (one).
I am using:
Server version: 5.1.46-community
MySQL Community Server (GPL)
Visual Studio 2008, version 9.
MySQL Connector C++ 1.0.5
My table description:
mysql> describe picture_image_data;
+---------------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------------+------------------+------+-----+---------+----------------+
| ID_Image_Data | int(10) unsigned | NO | PRI | NULL | auto_increment |
| Image_Data | mediumblob | YES | | NULL | |
+---------------+------------------+------+-----+---------+----------------+
2 rows in set (0.19 sec)
Results using MySQL monitor:
mysql> select ID_Image_Data
-> from picture_image_data;
+---------------+
| ID_Image_Data |
+---------------+
| 1 |
+---------------+
1 row in set (0.00 sec)
mysql> SELECT LAST_INSERT_ID();
+------------------+
| LAST_INSERT_ID() |
+------------------+
| 0 |
+------------------+
1 row in set (0.00 sec)
The Prepared statement:
INSERT INTO Picture_Image_Data
(ID_Image_Data, Image_Data)
VALUES
(?,
?);
The results above show that the ID_Image_Data field is one, but the LAST_INSERT_ID is zero. The table is created before this statement is executed, so this is the only record in the table.
Edit:
I am setting the ID field to zero and the next field to a C++ std::istream *. According to the MySQL Manual Page for LAST_INSERT_ID():
The value of LAST_INSERT_ID() is not changed if you set the AUTO_INCREMENT column of a row to a non-“magic” value (that is, a value that is not NULL and not 0).
The LAST_INSERT_ID() should return 1 since the ID value in the prepared statement is 0.
Do I need to make a prepared statement for fetching LAST_INSERT_ID?
{Searching the web showed to use a custom MySQL API, but that used PHP and futher comments said it needs another connection).

Answer 1

LAST_INSERT_ID would only work for auto generated primary key, that was created on auto_increment field. In your case, it looks like you are supplying the id explicitly, so last insert id is not set.
This is explicit:
mysql> insert into test (id, name) VALUES (5, 'test 2');
Query OK, 1 row affected (0.00 sec)
mysql> SELECT LAST_INSERT_ID();
+------------------+
| LAST_INSERT_ID() |
+------------------+
| 0 |
+------------------+
1 row in set (0.00 sec)
This is implicit:
mysql> insert into test (name) values ('test');
Query OK, 1 row affected (0.00 sec)
mysql> SELECT LAST_INSERT_ID();
+------------------+
| LAST_INSERT_ID() |
+------------------+
| 3 |
+------------------+
1 row in set (0.00 sec)

Answer 2

Looks like the issues is with the MySQL C++ connector.
LAST_INSERT_ID() returns 0 when
the ID field is null, explicit
insert.
LAST_INSERT_ID() returns 0 when
the ID field is not specified,
implicit insert.
I tried insert the BLOB (JPEG image) from the command line (monitor), and it works:
mysql> describe picture_image_data;
+---------------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------------+------------------+------+-----+---------+----------------+
| ID_Image_Data | int(10) unsigned | NO | PRI | NULL | auto_increment |
| Image_Data | mediumblob | YES | | NULL | |
+---------------+------------------+------+-----+---------+----------------+
2 rows in set (0.03 sec)
mysql> PREPARE blob_stmt
-> FROM 'INSERT INTO picture_image_data (ID_Image_Data, Image_Data) VALUES (?, LOAD_FILE(?))';
Query OK, 0 rows affected (0.02 sec)
Statement prepared
mysql> SET #id = 0;
Query OK, 0 rows affected (0.00 sec)
mysql> SET #c = 'KY_hot_brown_picture.jpg';
Query OK, 0 rows affected (0.00 sec)
mysql> EXECUTE blob_stmt USING #id, #c;
Query OK, 1 row affected (0.15 sec)
mysql> SELECT LAST_INSERT_ID();
+------------------+
| LAST_INSERT_ID() |
+------------------+
| 2 |
+------------------+
1 row in set (0.00 sec)
For now, the workaround is to use SQL statements to insert the BLOB with a prepared statement rather than the MySQL C++ Connector API.

Answer 3

You cannot expect issuing a SELECT LAST_INSERT_ID() on the mysql command line client to give you the last inserted value that was generated in your C++ code.
LAST_INSERT_ID() gives you the last autogenerated ID on the given connection. Obviously your C++ program and the mysql client uses 2 different connections to the mysql server.
(and LAST_INSERT_ID() should be used after an INSERT too, don't have other SQL statements inbetwwen the INSERT and SELECTLAST_INSERT_ID())