Return NEWID() from a SQL Query

Lany · 19 Dec 2019, 09:59

Hello,

I need the new id "NEWID()" created in this SQL Query, how can I get it?

QSqlQuery query;
query.exec("INSERT INTO TBL_TEST (TEST_ID, TEST_01) VALUES (NEWID(), '0');");

I tried something like this without success

QSqlQuery query;
query.exec("DECLARE @myid UNIQUEIDENTIFIER;"
           "SET @myid = NEWID();"
           "INSERT INTO TBL_TEST (TEST_ID, TEST_01) VALUES (@myid, '0');"
           "OUTPUT @myid;");
query.next();
qDebug() << query.value(0).toString();

Thanks.

JonB · L Lany 19 Dec 2019, 09:40

@Lany
MySQL != MS SQL, NEWID() does not exist. MySQL has LAST_INSERT_ID. I assume you mean TEST_ID is an autoincrement column:

QSqlQuery query;
query.exec("INSERT INTO TBL_TEST (TEST_01) VALUES ('0');"
           "SELECT LAST_INSERT_ID();");
query.next();
qDebug() << query.value(0).toString();

Lany · 19 Dec 2019, 10:44

Thank you for your answer,!
TEST_ID is not an autoincrement column, this is why I have to manage the creation of IDs.

JonB · L Lany 19 Dec 2019, 10:23

@Lany
Then say what your NEWID() is?

If your original code was broadly correct in that respect, then try the last line as SELECT @myid; instead of OUTPUT @myid;.

Lany · 19 Dec 2019, 12:07

I'm not a expert in SQL, I started to work in this project (and SQL) at the start of this week.
Here's the full code.

QSqlDatabase db = QSqlDatabase::addDatabase("QODBC");
db.setConnectOptions();
db.setDatabaseName("Driver={SQL Server};Server=" + m_str_adresseBaseSQL
                   + ";Database=" + m_str_nomBaseQSL + ";Uid=" + m_str_nomUtilisateur 
                   + ";Pwd=" + m_str_passUtilisateur + ";");

if (db.open()){
    QSqlQuery query;
    query.exec("DECLARE @myid UNIQUEIDENTIFIER;"
	       "SET @myid = NEWID();"
	       "INSERT INTO TBL_TEST (TEST_ID, TEST_01) VALUES (@myid, '0');"
	       "SELECT @myid;");
    qDebug() << query.next();
    qDebug() << query.value(0).toString();
    db.close();
}

And the debug output:

false
QSqlQuery::value: not positioned on a valid record
""

JonB · L Lany 19 Dec 2019, 11:35

@Lany
https://doc.qt.io/qt-5/qsqlquery.html#exec-1 also returns a bool value. Check that. When you discover it's returning false, debug out https://doc.qt.io/qt-5/qsqlquery.html#lastError.

Lany · 19 Dec 2019, 12:49

Here's the result of

qDebug() << query.exec("DECLARE @myid UNIQUEIDENTIFIER;"
                       "SET @myid = NEWID();"
                       "INSERT INTO TBL_TEST (TEST_ID, TEST_01) VALUES (@myid, '0');"
                       "SELECT @myid;");
qDebug() << query.next();
qDebug() << query.value(0).toString();
qDebug() << query.lastError().text();

Debug output:

true
false
QSqlQuery::value: not positioned on a valid record
""
" "

JonB · L Lany 19 Dec 2019, 12:39

@Lany
If QSqlQuery::next() is returning false I would see what query.lastError() on the immediately following line returns (I don't know whether that gets set, try it). I would read https://doc.qt.io/qt-5/qsqlquery.html#next, where restrictions are mentioned, e.g. for all I know/I suspect that for your statement https://doc.qt.io/qt-5/qsqlquery.html#isSelect is returning false.

Christian Ehrlicher · wrote on 19 Dec 2019, 13:32

I'm unsure if the qt mysql driver can handle multiple queries - I would guess no.

Lany · 19 Dec 2019, 15:00

I tried this

qDebug() << query.exec("DECLARE @myid UNIQUEIDENTIFIER;"
                       "SET @myid = NEWID();"
                       "INSERT INTO TBL_TEST (TEST_ID, TEST_01) VALUES (@myid, '0');"
                       "SELECT @myid;");
qDebug() << query.lastError().text();
qDebug() << query.isActive();
qDebug() << query.isSelect();
qDebug() << query.next();
qDebug() << query.value(0).toString();

the result:

true
" "
true
false
false
QSqlQuery::value: not positioned on a valid record
""

The query is not in a SELECT state, as mentioned by Christian, I think this driver can't handle multiple query.
I'm going to look for another solution.

Thanks!

KroMignon · L Lany 19 Dec 2019, 14:39

@Lany said in Return NEWID() from a SQL Query:

I'm going to look for another solution.

Perhaps you can try to send the SQL statement through QSqlDatabase::exec() ?

Mucip · wrote on 19 Dec 2019, 15:02

Hi,
I think you want to insert a record and get the record serila number from DB.
I guess it depends of what you use as database but in my case I use PostgreSQL and in this situation you have good SQL command like below:

//Yeni kaydet yapılıyor...
    QSqlQuery kayitDb(baglanti::mdb());
    kayitDb.prepare("INSERT INTO teklif(teklif_no, teklif_tarih, teklif_tip, aciklama, cari_kod, teslim_sure, odeme_tip, odeme_vade, teklif_kur, proje_kod) "
                    "VALUES(:teklif_no, :teklif_tarih, :teklif_tip, :aciklama, :cari_kod, :teslim_sure, :odeme_tip, :odeme_vade, :teklif_kur, :proje_kod) RETURNING sira_no;");

    kayitDb.bindValue(":teklif_no", ui->lETeklifNo->text());
    kayitDb.bindValue(":teklif_tarih", ui->dateTeklifTarih->date());
    kayitDb.bindValue(":teklif_tip", ui->lETeklifTip->text() );
    kayitDb.bindValue(":aciklama", ui->plainAciklama->toPlainText());
    kayitDb.bindValue(":cari_kod", ui->lECariKod->text().toInt());
    kayitDb.bindValue(":teslim_sure", ui->lETeslim->text());

    kayitDb.bindValue(":odeme_tip", ui->cBOdeme->currentText() );
    kayitDb.bindValue(":odeme_vade", ui->lEVade->text() );
    kayitDb.bindValue(":teklif_kur", ui->comboKur->currentText() );



     //Sending and returning serial ID...
    if(kayitDb.exec() && kayitDb.first())
    {
        int belgeSiraNo = kayitDb.value(0).toInt();
         ui->lESiraNo->setText(kayitDb.value(0).toString());


            if(detayKaydet(belgeSiraNo))
            {
                //İşlem sonu
                QMessageBox::information(this, "Tamamdır :)", "Fiş: " + ui->lESiraNo->text() + " sıra numarası ile kaydedildi.");
                ekranTemizle();
                iptalKonum();
            }

    } else
    {
        QMessageBox::critical(this, "Hata", "Veritabanına ulaşılamadı!\n"+kayitDb.lastError().text() );
        return;
    }

You're sending INSERT sql and reading returning serila value.

Regards,
Mucip:

kshegunov · L Lany 19 Dec 2019, 09:40

Just use the api, here you go: https://doc.qt.io/qt-5/qsqlquery.html#lastInsertId
There's little sense in trying to emulate something that's not standard and is already implemented in the driver.

Lany · 19 Dec 2019, 15:37

@kshegunov
The ID is generated by the db not by "me"

query.exec("INSERT INTO TBL_TEST (TEST_ID, TEST_01) VALUES (NEWID(), '0');");
qDebug() << query.lastInsertId().toString();

result:

"0"

In the db I have something like this :

315FD979-F300-4493-A0B9-4B5FE64A8F45

kshegunov · L Lany 19 Dec 2019, 15:34

@Lany said in Return NEWID() from a SQL Query:

The ID is generated by the db not by "me"

Yes, that's why the client library and the driver on top of it knows about it and can give it back to you. It's not necessary to do a query to emulate the behavior.

PS. You need to handle the variant you got properly, not just blindly convert it to a string.

qDebug() << query.lastInsertId().type();

should help. Also, please make sure that TEST_ID is a primary key in the database (i.e. is properly indexed).

Lany · 19 Dec 2019, 15:49

@kshegunov
The returned type is :

QVariant::double

TEST_ID is a primary key (PK, uniqueidentifier, not null)
If I try this

qDebug() << query.lastInsertId().toDouble();

The returned value is :

kshegunov · L Lany 19 Dec 2019, 15:47

What database engine is this? MySQL, PgSQL, MSSQL?

Lany · 19 Dec 2019, 16:04

Microsoft SQL server 2014

kshegunov · L Lany 19 Dec 2019, 15:58

Right, sorry I was misled about the talk about MySql. Anyways, you really should auto-generate the id, not insert it manually (probably not the problem here, just saying). I haven't worked with MS for ages. Check if the driver supports lastInstertId at all.

qDebug() << db.driver()->hasFeature(QSqlDriver::LastInsertId);

If it doesn't then you're stuck to using non-standard queries. That means once you run the insert, you run a second query to fetch the inserted id.