Query in QT doesn't get any data-CodePudding

This is rows in my table.

With this code, I get "in" in console.

QSqlQuery qry;
qry.prepare("SELECT * FROM user");
qry.exec();
if(qry.size() > 0)
    qInfo() << "in";
else
    qInfo() << "error";

But with this code, I get "error".

QSqlQuery qry;
qry.prepare("SELECT age FROM user");
qry.exec();
if(qry.size() > 0)
    qInfo() << "in";
else
    qInfo() << "error";

CodePudding user response：

Try

QSqlQuery qry;
qry.prepare("SELECT age FROM \"user\"");
qry.exec();

The problem is with the table name. Since user is a reserved word, some tools (PgAdmin) automatically add double quotes to the name "user" and you have to use double quotes when applying to the table. Unfortunately user in Postgres is a function (equivalent to current_user) hence the first query returns a row without error.

The best solution is to rename the table and not use reserved words as Postgres identifiers (the name of a table, column, view, function, etc).

CodePudding user response：

QSqlQuery qry;
qry.prepare("SELECT age FROM user");
if(qry.exec()) {
    while(qry.next()) {
        qInfo()<<"in";
    }
} else {
    qInfo()<<"error";
}