问题
I've been developing an asp.net web app using VS studio. I'm using SQL Server Express. During development I have been testing my web app on my server.
Every time that I need to update my database I would simply delete my old database (located on my server) and upload my new DB. Since I'm only testing, and my app has no users, it hasn't been a problem.
Problem:
Once my site goes live I don't know how to make changes to my DB. Obviously I wont be able to simply delete it as it will contain user data. So how do people typically update a live DB. That is, lets say my site is live and now I need to add more tables and stored procedures to my DB. How would i do this on a live site?
回答1:
To make changes to a production database, you'd:
- Try to schedule an outage when the least number of users will be affected, posting information so users are aware prior to
- Use data definition language (DDL) scripts to make the changes to the database tables, and potentially data manipulation language (DML) scripts to massage existing data into what the changes need.
The scripts necessary for step 2 should have been tested in Development and Test/QA environments to ensure as few issues as possible are experienced in the Production system. Backups that allow you to restore the database to previous versions of the application are required for both the Development and Test/QA environments.
回答2:
You either need to:
- Update your database at a time when no-one will be using the site. OR
- Ensure that your updates do not affect the operation of the site.
The second option involves giving any new non-NULLable columns sensible defaults, ensuring that all INSERT statements use column lists (e.g. INSERT INTO dbo.MyTable (col1, col2, col3) VALUES (...)) and ensuring that new stored procedure parameters have defaults. This is not an exhaustive list, but a good start.
回答3:
Mostly we create release scripts whereby the changes are scripted out and repeatable. So you will see things like
IF NOT EXISTS( SELECT * FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'myTableName'
AND COLUMN_NAME = 'myColumnName')
BEGIN
ALTER TABLE myTableName
ADD myColumnName varchar(50)
END
You can tell which objects have changed with stuff like:
SELECT
[name],
create_date,
modify_date
FROM sys.tables
ORDER BY
modify_date DESC
Some people use RedGate software to compare the 2 different database, but there is a cost to that.
回答4:
It depends on that kinds of changes you want to make to your live database.
In your question you only talk about adding new tables and stored procedures.
As long as you only add new stuff (tables, sprocs, or even new columns to existing tables) you don't have to do anything special, because SQL Server can do this while the database is in use and the changes don't affect your users because their version of your app doesn't even know about your newly added stuff.
On the other hand, it gets way more complicated if you change or even delete existing stuff.
There is a great chance that this will be a breaking change for your app, as it will probably stop working when tables look different than it expects or if it tries to access tables/sprocs that don't exist anymore.
(Even if you only add new stuff like I said in the beginning - you will probably want to update your app anyway, so it can actually USE the new stuff in the database)
So you probably will need to make your database changes AND deploy a new version of your app as well, both at the same time.
I'm no ASP.NET expert, but as far as I know it's not possible to update an ASP.NET app without all active users getting kicked out.
So in this case you would have to do what OMG Ponies already said: choose a time when the least possible number of users is affected, and/or inform your users early enough about the scheduled outage.
来源：https://stackoverflow.com/questions/6004993/how-to-make-live-changes-to-sql-server-express