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Say there is a database with 100+ tables and a major feature is added, which requires 20 of existing tables to be modified and 30 more added. The changes were done over a long time (6 months) by multiple developers on the development database. Let's assume the changes do not make any existing production data invalid (e.g. there are default values/nulls allowed on added columns, there are no new relations or constraints that could not be fulfilled).
What is the easiest way to publish these changes in schema to the production database? Preferably, without shutting the database down for an extended amount of time.
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To change the schema of a table by using SQL Server Management Studio, in Object Explorer, right-click on the table and then click Design. Press F4 to open the Properties window. In the Schema box, select a new schema. ALTER SCHEMA uses a schema level lock.
You can use DDL to add, modify, or remove schema objects as the database is running. For a list of all valid DDL you can use, see Appendix A, Supported SQL DDL Statements. You can do the following types of schema changes: Modifying Tables — You can add, modify (alter), and remove (drop) table columns.
Write a T-SQL script that performs the needed changes. Test it on a copy of your production database (restore from a recent backup to get the copy). Fix the inevitable mistakes that the test will discover. Repeat until script works perfectly.
Then, when it's time for the actual migration: lock the DB so only admins can log in. Take a backup. Run the script. Verify results. Put DB back online.
The longest part will be the backup, but you'd be crazy not to do it. You should know how long backups take, the overall process won't take much longer than that, so that's how long your downtime will need to be. The middle of the night works well for most businesses.
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