Tutorial by Examples: database



Creating a database in a particular location. If we dont specify any location for database its created in warehouse directory. CREATE DATABASE IF NOT EXISTS db_name COMMENT 'TEST DATABASE' LOCATION /PATH/HDFS/DATABASE/;
The Firebase Realtime Database allows ordering and querying data. For small data sizes, the database supports ad hoc querying, so indexes are generally not required during development. Before launching your app though, it is important to specify indexes for any queries you have to ensure they contin...
Another use of RODBC is in connecting with SQL Server Management Database. We need to specify the 'Driver' i.e. SQL Server here, the database name "Atilla" and then use the sqlQuery to extract either the full table or a fraction of it. library(RODBC) cn <- odbcDriverConnect(connect...
The following example is from 0.5 - 0.7 days, and illustrates how to log an error when the database hasn't populated the client side cursor yet. Template.landingPage.postsList = function(){ try{ return Posts.find(); }catch(error){ //color code the error (red) console.error(erro...
To use multiple databases in Django, just specify each one in settings.py: DATABASES = { 'default': { 'NAME': 'app_data', 'ENGINE': 'django.db.backends.postgresql', 'USER': 'django_db_user', 'PASSWORD': os.environ['LOCAL_DB_PASSWORD'] }, 'users': {...
The normal obj.save() method will use the default database, or if a database router is used, it will use the database as specified in db_for_write. You can override it by using: obj.save(using='other_db') obj.delete(using='other_db') Similarly, for reading: MyModel.objects.using('other_db').al...
Create Oracle error log table ERR$_EXAMPLE for existing EXAMPLE table: EXECUTE DBMS_ERRLOG.CREATE_ERROR_LOG('EXAMPLE', NULL, NULL, NULL, TRUE); Make writing operation with SQL: insert into EXAMPLE (COL1) values ('example') LOG ERRORS INTO ERR$_EXAMPLE reject limit unlimited;
You'll need to separate out your application layer from your database layer, and that means specifying the MONGO_URL. Which means running your app through the bundle command, uncompressing it, setting environment variables, and then launching the project as a node app. Here's how... #make sure you...
There's two great utilities for black-box analysis of databases. First is variety.js, which will give you a high-level overview. The second is schema.js, which will let you dig into the collections for more detail on the individual fields. When inheriting a production Mongo database, these two util...
The --url flag can be tricky to use. There is a 60 second window to authenticate, and then the username/password randomly resets. So be sure to have robomongo open and ready to configure a new connection when you run the command. # get the MONGO_URL string for your app meteor mongo --url $METEOR...
Same thing as before, but you have to copy the info into the mongodump command. You have to run the following commands rediculously fast, and it requires hand/eye coordination. Be warned! This is a rediculously hacky! But fun! Think of it as a video game! :D # get the MONGO_URL string for your app ...
Mongo supports database-to-database copying, which is useful if you have large databases on a staging database that you want to copy into a local development instance. // run mongod so we can create a staging database // note that this is a separate instance from the meteor mongo and minimongo ins...
Preallocation. Mongo sets aside disk-space in empty containers, so when the time comes to write something to disk, it doesn't have to shuffle bits out of the way first. It does so by a doubling algorithm, always doubling the amount of disk space preallocated until it reaches 2GB; and then each preal...
library(RODBC) con <- odbcDriverConnect("driver={Sql Server};server=servername;trusted connection=true") dat <- sqlQuery(con, "select * from table"); close(con) This will connect to a SQL Server instance. For more information on what your connection string should loo...
CREATE DATABASE LINK dblink_name CONNECT TO remote_username IDENTIFIED BY remote_password USING 'tns_service_name'; The remote DB will then be accessible in the following way: SELECT * FROM MY_TABLE@dblink_name; To test a database link connection without needing to know any of the objec...
Query can be used instead of table in import operation: sqoop import --query 'select Id,Message from TestTable where $CONDITIONS' --where 'id>100' --connect "jdbc:sqlserver://192.168.1.100:1433;database=Test_db --username user -–pas...
In the Project.pro file we add : CONFIG += sql in MainWindow.h we write : #include <QMainWindow> #include <QSql> #include <QDebug> namespace Ui { class MainWindow; } class MainWindow : public QMainWindow { Q_OBJECT public: explicit MainWindow(QWidget...
Dropping the database is a simple one-liner statement. Drop database will delete the database, hence always ensure to have a backup of the database if required. Below is the command to drop Employees Database DROP DATABASE [dbo].[Employees]
Option Compare Binary Binary comparison makes all checks for string equality within a module/class case sensitive. Technically, with this option, string comparisons are performed using sort order of the binary representations of each character. A < B < E < Z < a < b < e < z ...

Page 3 of 10