let's image that one creates an H2 database with table, indexes, etc... Is there an easy way to extract a SQL script to recreate the structure of this database in another H2 database?
I am not referring to the content of the tables, indexes, etc... I am just interested in the general structure of the database to replicate it elsewhere. Thanks.
I would use SCRIPT NODATA (returns a result set) or SCRIPT NODATA TO 'fileName'.
Related
I try to update my table in Cassandra database. Right now I have table which looks like
foo(id, email) - email text type
I want to update the table to something like
foo(id, emails) - emails list of text type
I added new column
ALTER TABLE foo ADD emails set <text>;
but I don't know how to migrate value from email column to emails.
I am not very familiar with your domain, however you have to tell Cassandra how to create the new list of emails. Take a look at COPY if you don't have too many records. You can
Add a new column
Use copy to export your existing data using COPY TO
Apply your transformations on the exported data
Use COPY FROM to upload your new data.
If you have to do this update in real time while your table is growing, this solution won't work.
Cassandra don't have a native solution to do such operation.
Maybe you can create a simple migration program with your favorite programming language and follow these steps :
Create the new column in cassandra (with ALTER command).
Execute the migration program.
Delete the old column in cassandra.
The program it self will take all record from cassandra one by one an apply the transformation.
I am recreating a web app in Django that was running in a server but it was terminated, fortunately, I did a backup of all the code. My problem comes with the database because but I do not know how to transfer all the data from the old db.sqlite3 Django database web app into the new one.
I found a similar question as mine Django: transfer data from one database to another but the user wanted to transfer data from specific columns because their models.pyfrom the old and new databases were slightly different. In my case, my models.py from the old and new databases are the same.
Alternatives
I am using the DB Browser for SQLite to explore the content of the old database and I could add manually each row into the Django administration but this will take me too much time.
I could copy the old db.sqlite and replace it in the new web app because the models.py file remains the same but this solution is not appropriate IMO, this solution is rude and I think it goes against the good practices of Software.
How should I proceed for transferring data from the old database to the new one?
This seems like a one time copy of one db to another. I don't see how this goes against good software practice unless you have to be copying this db frequently. I've done it before when migrating servers and it doesn't cause any issues assuming the two instances of the application are the same build.
I was able to do some minor tricks in order to solve my problem because there is not a straightforward functionality that allows you to transfer all your data from two sqlite databases in Django. Here is the trick I did:
Download the sqlite db browser to explore and export the contents of your old database in a .csv file. Open you database with sqlite db browser and hit on the tables option and you will see all your tables, then do a right click on any of those and hit the export as a csv file option to generate the csv file (name_of_your_csv_file.csv). The other alternative is to use the sqlite3.exe to open your database in cmd or powershell and then doing the export with:
.tables #this lets you explore your available tables
headers on
mode csv
output name_of_your_csv_file.csv
2.There are two choices up to this point: You can either insert all the records at once to your new database or you can drop your existing tables from the new database and then recreate them and import the .csv file. I went for the drop option because there were more than 100 records to migrate.
# sqlite3
# check the structure of your table so you can re-create it
.schema <table_name>
#the result might be something like CREATE TABLE IF NOT EXISTS "web_app_navigator_table" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT, "ticket" varchar(120) NOT NULL);
#drop the table
drop table web_app_navigator_table
#re-create the table
create table web_app_navigator_table(id integer not null primary key autoincrement, ticket varchar(120) not null);
#do the import of the csv file
.import C:/Users/a/PycharmProjects/apps/navigator/name_of_your_csv_file.csv table_name_goes_here
You might see an error such as csv:1: INSERT failed datatype mismatch but this indicates that the first row of your csv file was not inserted because it contains the headers of the exported data from your old database.
What options do I have to migrate data to hosted with Heroku Postgres Database?
I have Django app and my client is migrating is moving from his existing software will most likely produce data in excel format. I will figure out the data model and data conversion I just need to know what tools to use to do the actual update of the DB.
Your Question is probably too broad for this site. But briefly, for Postgres in general…
INSERT
The usual way to put data into a SQL database is the INSERT command.
COPY FROM
To add data in bulk rather than one record at a time, call COPY FROM. You specify a file to be imported.
I think this is a recurrent question in the Internet, but unfortunately I'm still unable to find a successful answer.
I'm using Ruby on Rails 4 and I would like to create a model that interfaces with a SQL query, not with an actual table in the database. For example, let's suppose I have two tables in my database: Questions and Answers. I want to make a report that contains statistics of both tables. For such purpose, I have a complex SQL statement that takes data from these tables to build up the statistics. However the SELECT used in the SQL statement does not directly take values from neither Answers nor Questions tables, but from nested SELECTs.
So far I've been able to create the StatItem model, without any migration, but when I try StatItem.find_by_sql("...nested selects...") the system complains about unexisting table stat_items in the database.
How can I create a model whose instance's data is retrieved from a complex query and not from a table? If it's not possible, I could create a temporary table to store the data in there. In such case, how can I tell the migration file to not create such table (it would be created by the query)?
How about creating a materialized view from your complex query and following this tutorial:
ActiveRecord + PostgreSQL Materialized Views
Michael Kohl and his proposal of materialized views has given me an idea, which I initially discarded because I wrongly thought that a single database connection could be shared by two processes, but after reading about how Rails processes requests, I think my solution is fine.
STEP 1 - Create the model without migration
rails g model StatItem --migration=false
STEP 2 - Create a temporary table called stat_items
#First, drop any existing table created by older requests (database connections are kept open by the server process(es).
ActiveRecord::Base.connection.execute('DROP TABLE IF EXISTS stat_items')
#Second, create the temporary table with the desired columns (notice: a dummy column called 'id:integer' should exist in the table)
ActiveRecord::Base.connection.execute('CREATE TEMP TABLE stat_items (id integer, ...)')
STEP 3 - Execute an SQL statement that inserts rows in stat_items
STEP 4 - Access the table using the model, as usual
For example:
StatItem.find_by_...
Any comments/improvements are highly appreciated.
I am working on a project that needs to be able to create dynamic queries into an H2 database. This also includes a full text search with built-in H2 logic, tables, and triggers.
I have been trying to figure out how to add that full-text search into my CriteriaQuery but keep running into the road block that the tables used aren't entities in my model. I could add them as entities, but I don't want them created automatically by EclipseLink when a new database file is created since there is a function in H2 that creates the tables and does other necessary housekeeping.
I had tried the path of creating a view to query the full text tables to give me the information I need in the format I need. But I still keep running into the same problem that that view is not an Entity.
Has anyone encountered this situation before and/or figured out a way around it?
Thanks!