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Selecting data from mysql using qt?

  • i add #include <QVariant>

    now it is saying
    QSqlQuery::exec: database not open

  • Try to use QSqlQuery::lastError() for find problem

  • what is the problem now in my code why it is not opening database?

  • Did you leave

    //bool ok =;


  • well i changed my code to this and added lastError as well

    #include <QApplication>
    #include <QSqlDatabase>
    #include <QSqlError>
    #include <QSqlQuery>
    #include <QDebug>
    #include <QString>
    #include <QVariant>
    //#include <QtCore>
    //#include <QtSql>
    //#include "../connection.h"
    #include "db.h"

    int main(int argc, char *argv[])
    QCoreApplication a(argc, argv);

    QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
    //bool ok =;
    QSqlQuery query;
    query.exec&#40;"SELECT firstname,lastname FROM testTable"&#41;;
    while( {
        QString firstName = query.value(0).toString();
        QString secondName = query.value(1).toString();
        qDebug() << "First Name: " << firstName << "Last Name:" << secondName;
        qDebug() << db.lastError();
    return a.exec&#40;&#41;;


    it still says QSqlQuery::exec: database not open

  • it is still as commented
    [quote author="Antonio Di Monaco" date="1286818410"]Did you leave

    //bool ok =;


  • Try uncomment line 23

  • i uncomment line 23 and comment everything below line 23 then it just says
    Starting /home/zafar/c++/dbExample-build-desktop/dbExample...

    and stucks there

  • OH! You use SQL code before
    Are you sure?

    Create standart QT GUI application and wrote sql code in mainwindow module.

  • i am new to qt. how can i create Qt Gui App and do you mean i should write sql code in mainwindow.h file?

  • right now i have three files. db.h, db,cpp and main.cpp

  • Run QT Creator.
    Use menu File/new file or project.
    Select QT Gui application.
    and select SQL checkbox
    and write sql code in MainWindow.cpp
    and see SQL Example please

  • well i tried "File/new file or project and select qt gui app" but i ddint find any sql checkbox anywhere in creating new project

  • no coments...
    How can I send you screenshot?

  • you can add pictures here as screenshots or if you want my email address i ll give you that as well for screenshots

  • anyone who can help?

  • well i dont have that option. here is what i get
    when i click file/new file or project then this screenshot
    "Your text to link here...":
    then i keep clicking next getting the follwoing screenshots
    "Your text to link here...":
    "Your text to link here...":
    "Your text to link here...":
    "Your text to link here...":

  • Well, it should make no problem to have SQL query before exec(), at least I don't have any problem with that.

    Let's get back to square one:
    You said if you uncomment the
    @bool ok =;@
    then your program hangs. Can we see the value of 'ok'?
    @qDebug() << ok;@
    My guess is probably you have problems granting the rights in mysql when you've created the table... have you made
    @GRANT ALL ON testTwo.* to 'root'at'localhost' IDENTIFIED BY 'somepassword';@
    (Ouch please replace the 'at' with the 'at' sign, the forum motor uses it for code tags, I don't know how to write it... I hope it's not confusing.
    I'm not sure if you can do it with empty password, I guess yes, but I never do that.)

  • i now put password for root at localhost.
    when i place qDebug() << ok then it displays this
    QSqlQuery::exec: database not open

    false might be the value of ok.

  • Are you able to connect to your DB from shell?

  • i dont know how to connect to my DB from shell. I install xampp which is easy for me to manage my databases.
    how can i connect from shell?

  • @mysql -h host -D dbname -u user@

    I guess your can omit host parameter if you are connecting to localhost. You might need to specify "-p password" switch also (depends on mysql configuration).

  • i think i did not install any mysql client. bcause it displays this output
    root@zafar-laptop:/# mysql -h localhost -D testTwo -u root -p xxxxxx
    The program 'mysql' can be found in the following packages:

    • mysql-client-core-5.1
    • mysql-client-5.0
    • mysql-cluster-client-5.1
      Try: apt-get install <selected package>

  • Run
    @dpkg --list | grep mysql@
    and post the output for this command.

  • here it is
    root@zafar-laptop:/# dpkg --list | grep mysql
    ii libmysqlclient-dev 5.1.41-3ubuntu12.6 MySQL database development files
    ii libmysqlclient16 5.1.41-3ubuntu12.6 MySQL database client library
    ii mysql-common 5.1.41-3ubuntu12.6 MySQL database common files (e.g. /etc/mysql


  • How did you create your database? I don't see any mysql server either.

  • well i download xampp and install it. i created database using phpmyadmin.

  • i install xampp in this folder /opt/lampp

    and my database is in /opt/lampp/var/mysql

  • Ok, I see. What is the location of your XAMPP installation? try to find the mysql binary there. And use the whole path (since I assume it is not in PATH) when connecting, i.e.

    @/path/to/xampp/bin/mysql -D dbname -u username@

    UPD: Didn't notice the location of xampp. then try (I guess it would be like this) @/opt/lampp/bin/mysql@

  • now here it what it says
    root@zafar-laptop:/# /opt/lampp/bin/mysql -D testTwo -h localhost -u root -p 123456
    Enter password:
    ERROR 1049 (42000): Unknown database '123456'
    i am providing the right pw

  • Try not passing -p switch. I guess you will be prompted to type in your password.
    @/opt/lampp/bin/mysql -u root testTwo@

  • now it output is Access Denied
    root@zafar-laptop:/# /opt/lampp/bin/mysql -u root testTwo
    ERROR 1045 (28000): Access denied for user 'root'at'localhost' (using password: NO)

  • I'm sorry i just confused you with my last post.

    @/opt/lampp/bin/mysql -u root -p 123456 testTwo@

    I thought that mysql would prompt you but it didn't.

  • Do it this way, then it will prompt for a password:

    @/opt/lampp/bin/mysql -D testTwo -h localhost -u root -p

  • i got a big ouput here but i have not seen any errors in this. when i try to post whole output this forum didnt allow me to post more than 6000 characters

  • Cut it into pieces or use something like pastebin.

  • ok here it is
    root@zafar-laptop:/# /opt/lampp/bin/mysql -u root -p 123456 testTwo
    /opt/lampp/bin/mysql Ver 14.14 Distrib 5.1.41, for pc-linux-gnu (i686) using EditLine wrapper
    Copyright 2000-2008 MySQL AB, 2008 Sun Microsystems, Inc.
    This software comes with ABSOLUTELY NO WARRANTY. This is free software,
    and you are welcome to modify and redistribute it under the GPL license
    Usage: /opt/lampp/bin/mysql [OPTIONS] [database]
    -?, --help Display this help and exit.
    -I, --help Synonym for -?
    --auto-rehash Enable automatic rehashing. One doesn't need to use
    'rehash' to get table and field completion, but startup
    and reconnecting may take a longer time. Disable with
    -A, --no-auto-rehash
    No automatic rehashing. One has to use 'rehash' to get
    table and field completion. This gives a quicker start of
    mysql and disables rehashing on reconnect. WARNING:
    options deprecated; use --disable-auto-rehash instead.
    -B, --batch Don't use history file. Disable interactive behavior.
    (Enables --silent)
    Directory where character sets are.
    --column-type-info Display column type information.
    -c, --comments Preserve comments. Send comments to the server. The
    default is --skip-comments (discard comments), enable
    with --comments
    -C, --compress Use compression in server/client protocol.
    -#, --debug[=#] This is a non-debug version. Catch this and exit
    --debug-check Check memory and open file usage at exit.
    -T, --debug-info Print some debug info at exit.
    -D, --database=name Database to use.
    Set the default character set.
    --delimiter=name Delimiter to be used.
    -e, --execute=name Execute command and quit. (Disables --force and history
    -E, --vertical Print the output of a query (rows) vertically.
    -f, --force Continue even if we get an sql error.
    -G, --named-commands
    Enable named commands. Named commands mean this program's
    internal commands; see mysql> help . When enabled, the
    named commands can be used from any line of the query,
    otherwise only from the first line, before an enter.
    Disable with --disable-named-commands. This option is
    disabled by default.
    -g, --no-named-commands
    Named commands are disabled. Use * form only, or use
    named commands only in the beginning of a line ending
    with a semicolon (;) Since version 10.9 the client now
    starts with this option ENABLED by default! Disable with
    '-G'. Long format commands still work from the first
    line. WARNING: option deprecated; use
    --disable-named-commands instead.
    -i, --ignore-spaces Ignore space after function names.


  • @
    --local-infile Enable/disable LOAD DATA LOCAL INFILE.
    -b, --no-beep Turn off beep on error.
    -h, --host=name Connect to host.
    -H, --html Produce HTML output.
    -X, --xml Produce XML output
    --line-numbers Write line numbers for errors.
    -L, --skip-line-numbers
    Don't write line number for errors. WARNING: -L is
    deprecated, use long version of this option instead.
    -n, --unbuffered Flush buffer after each query.
    --column-names Write column names in results.
    -N, --skip-column-names
    Don't write column names in results. WARNING: -N is
    deprecated, use long version of this options instead.
    -O, --set-variable=name
    Change the value of a variable. Please note that this
    option is deprecated; you can set variables directly with
    --sigint-ignore Ignore SIGINT (CTRL-C)
    -o, --one-database Only update the default database. This is useful for
    skipping updates to other database in the update log.
    --pager[=name] Pager to use to display results. If you don't supply an
    option the default pager is taken from your ENV variable
    PAGER. Valid pagers are less, more, cat [> filename],
    etc. See interactive help (\h) also. This option does not
    work in batch mode. Disable with --disable-pager. This
    option is disabled by default.
    --no-pager Disable pager and print to stdout. See interactive help
    (\h) also. WARNING: option deprecated; use
    --disable-pager instead.
    -p, --password[=name]
    Password to use when connecting to server. If password is
    not given it's asked from the tty.
    -P, --port=# Port number to use for connection or 0 for default to, in
    order of preference, my.cnf, $MYSQL_TCP_PORT,
    /etc/services, built-in default (3306).
    --prompt=name Set the mysql prompt to this value.
    --protocol=name The protocol of connection (tcp,socket,pipe,memory).
    -q, --quick Don't cache result, print it row by row. This may slow
    down the server if the output is suspended. Doesn't use
    history file.
    -r, --raw Write fields without conversion. Used with --batch.
    --reconnect Reconnect if the connection is lost. Disable with
    --disable-reconnect. This option is enabled by default.
    -s, --silent Be more silent. Print results with a tab as separator,
    each row on new line.
    -S, --socket=name Socket file to use for connection.
    --ssl Enable SSL for connection (automatically enabled with
    other flags). Disable with --skip-ssl.
    --ssl-ca=name CA file in PEM format (check OpenSSL docs, implies
    --ssl-capath=name CA directory (check OpenSSL docs, implies --ssl).
    --ssl-cert=name X509 cert in PEM format (implies --ssl).
    --ssl-cipher=name SSL cipher to use (implies --ssl).
    --ssl-key=name X509 key in PEM format (implies --ssl).
    Verify server's "Common Name" in its cert against
    hostname used when connecting. This option is disabled by
    -t, --table Output in table format.
    --tee=name Append everything into outfile. See interactive help (\h)
    also. Does not work in batch mode. Disable with
    --disable-tee. This option is disabled by default.
    --no-tee Disable outfile. See interactive help (\h) also. WARNING:
    option deprecated; use --disable-tee instead
    -u, --user=name User for login if not current user.
    -U, --safe-updates Only allow UPDATE and DELETE that uses keys.
    -U, --i-am-a-dummy Synonym for option --safe-updates, -U.
    -v, --verbose Write more. (-v -v -v gives the table output format).
    -V, --version Output version information and exit.
    -w, --wait Wait and retry if connection is down.
    --connect_timeout=# Number of seconds before connection timeout.
    Max packet length to send to, or receive from server
    Buffer for TCP/IP and socket communication
    --select_limit=# Automatic limit for SELECT when using --safe-updates
    --max_join_size=# Automatic limit for rows in a join when using
    --secure-auth Refuse client connecting to server if it uses old
    (pre-4.1.1) protocol
    --server-arg=name Send embedded server this as a parameter.
    --show-warnings Show warnings after every statement.

    Default options are read from the following files in the given order:
    /etc/xampp/my.cnf /opt/lampp/etc/my.cnf ~/.my.cnf
    The following groups are read: mysql client
    The following options may be given as the first argument:
    --print-defaults Print the program argument list and exit
    --no-defaults Don't read default options from any options file
    --defaults-file=# Only read default options from the given file #
    --defaults-extra-file=# Read this file after the global files are read


  • @
    Variables (--variable-name=value)
    and boolean options {FALSE|TRUE} Value (after reading options)

    auto-rehash FALSE
    character-sets-dir (No default value)
    column-type-info FALSE
    comments FALSE
    compress FALSE
    debug-check FALSE
    debug-info FALSE
    database (No default value)
    default-character-set latin1
    delimiter ;
    vertical FALSE
    force FALSE
    named-commands FALSE
    ignore-spaces FALSE
    local-infile FALSE
    no-beep FALSE
    host (No default value)
    html FALSE
    xml FALSE
    line-numbers TRUE
    unbuffered FALSE
    column-names TRUE
    sigint-ignore FALSE
    port 3306
    prompt mysql>
    quick FALSE
    raw FALSE
    reconnect TRUE
    socket /opt/lampp/var/mysql/mysql.sock
    ssl FALSE
    ssl-ca (No default value)
    ssl-capath (No default value)
    ssl-cert (No default value)
    ssl-cipher (No default value)
    ssl-key (No default value)
    ssl-verify-server-cert FALSE
    table FALSE
    user root
    safe-updates FALSE
    i-am-a-dummy FALSE
    connect_timeout 0
    max_allowed_packet 16777216
    net_buffer_length 16384
    select_limit 1000
    max_join_size 1000000
    secure-auth FALSE
    show-warnings FALSE


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