SQL: How to remove & update records in a table, sync'ing with a (Q)List data in order to decrease the burden on database/table? - sql

Question

I am using Qt and MS-Sql Server on Windows7 OS.
What I have is an MS-SQL database that I use to store data/info coming from equipment that is mounted in some vehicles.
There is a table in the database named TransactionFilesInfo - a table used to store information about transaction files from the equipment, when they connect to the TCP-server.
We are using this table as we are requested to avoid duplicate files. It happens (sometimes) when the remote equipment does NOT delete the transaction files after they are sent to the server. Hence, I use the info from the table to check [size and CRC] to avoid downloading duplicates.
Some sample data for TransactionFilesInfo table looks like this:
[TransactionFilesInfo]:
DeviceID FileNo FileSequence FileSize FileCRC RecordTimeStamp
10203 2 33 230 55384 2015-11-26 14:54:15
10203 7 33 624 55391 2015-11-26 14:54:15
10203 2 34 146 21505 2015-11-26 14:54:16
10203 7 34 312 35269 2015-11-26 14:54:16
10203 2 35 206 23022 2015-11-26 15:33:22
10203 7 35 208 11091 2015-11-26 15:33:22
10203 2 36 134 34918 2015-11-26 15:55:44
10203 7 36 104 63865 2015-11-26 15:55:44
10203 2 37 140 35466 2015-11-26 16:20:38
10203 7 37 208 62907 2015-11-26 16:20:38
10203 2 38 134 17706 2015-11-26 16:38:33
10203 7 38 104 42358 2015-11-26 16:38:33
11511 2 21 194 29913 2015-12-02 16:22:59
11511 7 21 114 30038 2015-12-02 16:22:59
On the other hand, every time a device connects to the server, it first sends a list of file information. The Qt application takes care of that.
The list contains elements like this:
struct FileInfo
{
unsigned short FileNumber;
unsigned short FileSequence;
unsigned short FileCRC;
unsigned long FileSize;
};
So, as an example (inspired by the table above) the connected device (DeviceID=10203) may say that it has the following files:
QList<FileInfo> filesList;
// here is the log4qt output...
filesList[0] --> FileNo=2 FileSeq=33 FileSize=230 and FileCRC=55384
filesList[1] --> FileNo=2 FileSeq=34 FileSize=146 and FileCRC=21505
filesList[2] --> FileNo=7 FileSeq=33 FileSize=624 and FileCRC=55391
filesList[3] --> FileNo=7 FileSeq=34 FileSize=312 and FileCRC=35269 ...
Well, what I need is a method to remove/delete, for a given DeviceID, all the records in the TransactionFilesInfo table, records that are NOT in the list sent by the remote device. Hence, I will be able to decrease the burden (size) on the database table.
Remark: For the moment I just delete (#midnight) all the records that are older than let's say 10 days, based on RecordTimeStamp field. So, the size of the table doesn't increase over an alarming level :)
Finally, to clarify it a little bit: I would mainly need help with SQL. Yet, I would not refuse any idea on how to do some related things/tricks on the Qt side ;)

Answer 1

The SQL to delete those records might look something like this:
DELETE FROM [SAMPLE DATA]
WHERE DeviceID = 10203
and 'File' + CONVERT(varchar(11),FileNo) + '_' +
RIGHT('000' + CONVERT(varchar(11),FileSequence),3)
NOT IN ('File2_033','File2_034','File7_033','File7_034',...)
If you wanted to delete all of them for a device, you could drop the code that looks at the FileNo and FileSequence so it is simply:
DELETE FROM [SAMPLE DATA]
WHERE DeviceID = 10203