SQL version control methodology

Question

There are several questions on SO about version control for SQL and lots of resources on the web, but I can\'t find something that quite covers what I\'m trying to do.

F

Answer 1

I struggled with this for several years before recently adopting a strategy that seems to work pretty well. Key points I live by:

• The database doesn't need to be independently versioned from the app
• All database update scripts should be idempotent

As a result, I no longer create any kind of version tables. I simply add changes to a numbered sequence of .sql files that can be applied at any given time without corrupting the database. If it makes things easier, I'll write a simple installer screen for the app to allow administrators to run these scripts whenever they like.

Of course, this method does impose a few requirements on the database design:

• All schema changes are done through script - no GUI work.
• Extra care must be taken to ensure all keys, constraints, etc.. are named so they can be referenced by a later update script, if necessary.
• All update scripts should check for existing conditions.

Examples from a recent project:

001.sql:

if object_id(N'dbo.Registrations') is null 
begin
    create table dbo.Registrations
    (
        [Id]                    uniqueidentifier not null,
        [SourceA]               nvarchar(50)     null,
        [SourceB]               nvarchar(50)     null,
        [Title]                 nvarchar(50)     not null,
        [Occupation]            nvarchar(50)     not null,
        [EmailAddress]          nvarchar(100)    not null,
        [FirstName]             nvarchar(50)     not null,
        [LastName]              nvarchar(50)     not null,
        [ClinicName]            nvarchar(200)    not null,
        [ClinicAddress]         nvarchar(50)     not null,
        [ClinicCity]            nvarchar(50)     not null,
        [ClinicState]           nchar(2)         not null,
        [ClinicPostal]          nvarchar(10)     not null,
        [ClinicPhoneNumber]     nvarchar(10)     not null,
        [ClinicPhoneExtension]  nvarchar(10)     not null,
        [ClinicFaxNumber]       nvarchar(10)     not null,
        [NumberOfVets]          int              not null,  
        [IpAddress]             nvarchar(20)     not null,
        [MailOptIn]             bit              not null,
        [EmailOptIn]            bit              not null,
        [Created]               datetime         not null,
        [Modified]              datetime         not null,
        [Deleted]               datetime         null
    );
end

if not exists(select 1 from information_schema.table_constraints where constraint_name = 'pk_registrations')
    alter table dbo.Registrations add
        constraint pk_registrations primary key nonclustered (Id);

if not exists (select 1 from sysindexes where [name] = 'ix_registrations_created')
    create clustered index ix_registrations_created
        on dbo.Registrations(Created);

if not exists (select 1 from sysindexes where [name] = 'ix_registrations_email')
    create index ix_registrations_email
        on dbo.Registrations(EmailAddress);

if not exists (select 1 from sysindexes where [name] = 'ix_registrations_email')
    create index ix_registrations_name_and_clinic
        on dbo.Registrations (FirstName,
                              LastName,
                              ClinicName);

002.sql

/**********************************************************************
  The original schema allowed null for these columns, but we don't want
  that, so update existing nulls and change the columns to disallow 
  null values
 *********************************************************************/

update dbo.Registrations set SourceA = '' where SourceA is null;
update dbo.Registrations set SourceB = '' where SourceB is null;
alter table dbo.Registrations alter column SourceA nvarchar(50) not null;
alter table dbo.Registrations alter column SourceB nvarchar(50) not null;

/**********************************************************************
  The client wanted to modify the signup form to include a fax opt-in
 *********************************************************************/

if not exists 
(
    select 1 
      from information_schema.columns
     where table_schema = 'dbo'
       and table_name   = 'Registrations'
       and column_name  = 'FaxOptIn'
)
alter table dbo.Registrations 
    add FaxOptIn bit null 
        constraint df_registrations_faxoptin default 0;

003.sql, 004.sql, etc...

At any given time I can run the entire series of scripts against the database in any state and know that things will be immediately brought up to speed with the current version of the app. Because everything is scripted, it's much easier to build a simple installer to do this, and it's adding the schema changes to source control is no problem at all.