SQL Server :: Compare Database Schemas

This is a script to list basic differences in table definitions between two databases.

Background Waffle
When we make database changes in a transactional system, we need to ensure that these won’t adversely affect our BI solution. Normally our developers give us this information when we plan which items to put into a release, so we can liaise with BI; unfortunately the developers machines are down at present due to a disaster at the data center of the company to whom we outsourced development. Since the changes for the release are already in our UAT environment (and only those changes are there), we could determine what would be changing in production by comparing the schemas of the two environments.

My first thought was to use the Database Comparison Tool that comes with Visual Studio. However whilst this does a great job for a developer looking for and resolving differences, it’s not so easy to communicate this information to others (i.e. giving a before and after image of columns side by side. You have to either click on each difference to get a definition of the before and after, then make notes or take screenshots, or you have to generate the DDL, in which case you don’t see the before picture; only the code to amend from the current to the to-be definition.

Instead I realised that I could simply pull the definitions of the tables & columns from SQL, compare these and list the differences; resulting in the code below.
This code can handle where both databases are on the same instance, or where they’re on different instances. For the latter scenario you’d need to create a linked server.
If you frequently compare different combinations of databases and want to avoid amending the instance and catalog names in the code each time you may want to look into views or synonyms (potentially aliases work too if the catalog name is consistent across instances).

Since our BI solution uses replication to get the data from the transactional system, I also included information on which columns were replicated; thus we can filter on those replicated to see just those which BI would be interested in, or can ignore replication to see all differences.


  1. We’re not comparing everything; only basic table and column data.
  2. The maxLength value gives length in bytes; not characters (see previous post on how to correct for this).
  3. There are probably other issues; this was a quick fix to resolve an immediate issue which worked for us; there may be issues we’ve not encountered (e.g. maybe the linked server only gives access to a subset of the tables; thus giving false responses)…


set transaction isolation level read uncommitted

;with uat as
       select TableName
       , c.Name ColumnName
       , ColType
       , c.max_length ColMaxLength
       , coalesce(c.is_nullable,0) ColIsNullable
       , c.scale ColScale
       , c.[precision] ColPrecision
       , coalesce(c.collation_name,'') ColCollation
       , c.is_replicated
       from [myUatDbServer\uatInstance].[myUatDbCatalog].sys.tables t
       inner join [myUatDbServer\uatInstance].[myUatDbCatalog].sys.columns c
              on c.object_id = t.object_id
       inner join [myUatDbServer\uatInstance].[myUatDbCatalog].sys.types ty
              on ty.system_type_id = c.system_type_id
              and ty.user_type_id = c.user_type_id
, prd as
       select TableName
       , c.Name ColumnName
       , ColType
       , c.max_length ColMaxLength
       , coalesce(c.is_nullable,0) ColIsNullable
       , c.scale ColScale
       , c.[precision] ColPrecision
       , coalesce(c.collation_name,'') ColCollation
       , c.is_replicated
       from [myProdDbServer\prodInstance].[myProdDbCatalog].sys.tables t
       inner join [myProdDbServer\prodInstance].[myProdDbCatalog].sys.columns c
              on c.object_id = t.object_id
       inner join [myProdDbServer\prodInstance].[myProdDbCatalog].sys.types ty
              on ty.system_type_id = c.system_type_id
              and ty.user_type_id = c.user_type_id
select coalesce(uat.TableName, prd.TableName) TableName
, coalesce(uat.ColumnName, prd.ColumnName) ColumnName
, case
       when prd.TableName is null and not exists (select top 1 1 from prd x where x.TableName = uat.TableName) then 'Add Table'
       when uat.TableName is null and not exists (select top 1 1 from uat x where x.TableName = prd.TableName)  then 'Remove Table'
       when prd.ColumnName is null then 'Add Column'
       when uat.ColumnName is null then 'Remove Column'
       else 'Change Column Definition'
end [AXtion] --our transaction system's Dynamics AX; I'm hilarious :S
, prd.ColType ColTypeFrom
, uat.ColType ColTypeTo
, prd.ColMaxLength ColMaxLengthFrom --not going to fuss about char byte size for now; just want to get a list of changes
, uat.ColMaxLength ColMaxLengthTo --not going to fuss about char byte size for now; just want to get a list of changes
, prd.ColIsNullable ColIsNullableFrom
, uat.ColIsNullable ColIsNullableTo
, prd.ColCollation ColCollationFrom
, uat.ColCollation ColCollationTo
, prd.ColPrecision ColPrecisionFrom
, uat.ColPrecision ColPrecisionTo
, prd.ColScale ColScaleFrom
, uat.ColScale ColScaleTo
, prd.is_replicated PrdIsReplicated --\_these aren't compared; just returned to make it easy to tell what's interesting to BI
, uat.is_replicated UatIsReplicated --/
from uat
full outer join prd
       on prd.TableName = uat.TableName
       and prd.ColumnName = uat.ColumnName
where prd.TableName is null
or uat.TableName is null
or prd.ColumnName is null
or uat.ColumnName is null
or (uat.ColType != prd.ColType)
or (uat.ColMaxLength != prd.ColMaxLength)
or (uat.ColIsNullable != prd.ColIsNullable) 
or (uat.ColCollation != prd.ColCollation) 
or (uat.ColPrecision != prd.ColPrecision) 
or (uat.ColScale != prd.ColScale)
order by coalesce(uat.TableName, prd.TableName) 
, coalesce(uat.ColumnName, prd.ColumnName) 


T-SQL: Generate Series: Getting a list of numbers in a given range.

Filed under: Microsoft, SQL Server, Technology — Tags: , , , , , , , , , — Developer42 @ 01:27

I recently came across the Postgres generate_series function whilst reading a blog post.
So far as I can tell, there’s no equivalent in T-SQL. To make up for this, I coded my own, making use of the recursive nature of common table expressions:

create function dbo.generate_series
	  @start bigint
	, @stop bigint
	, @step bigint = 1
	, @maxResults bigint = 0 --0 = unlimited
returns @results table(n bigint)

	--avoid infinite loop (i.e. where we're stepping away from stop instead of towards it)
	if @step = 0 return
	if @start > @stop and @step > 0 return
	if @start < @stop and @step < 0 return
	--ensure we don't overshoot
	set @stop = @stop - @step

	--treat negatives as unlimited
	set @maxResults = case when @maxResults < 0 then 0 else @maxResults end

	--generate output
	;with myCTE (n,i) as 
		--start at the beginning
		select @start
		, 1
		union all
		--increment in steps
		select n + @step
		, i + 1
		from myCTE 
		--ensure we've not overshot (accounting for direction of step)
		where (@maxResults=0 or i<@maxResults)
			   (@step > 0 and n <= @stop)
			or (@step < 0 and n >= @stop)
	insert @results
	select n 
	from myCTE
	option (maxrecursion 0) --sadly we can't use a variable for this; however checks above should mean that we have a finite number of recursions / @maxResults gives users the ability to manually limit this 

	--all good	

Example Usage:

--check we get expected results
select * from generate_series(1, 10, default, default)
select * from generate_series(10, 5, -1, default)
select * from generate_series(1, 10, 4, default)
select * from generate_series(1, 10, default, 2)
select * from generate_series(1, 10, 4, -1)

--check we don't get results if we have "invalid" input
select * from generate_series(1, 10, 0, default)
select * from generate_series(10, 1, default, default)
select * from generate_series(10, 5, 1, default)
select * from generate_series(1, 10, -4, default)

NB: Should you wish to generate a series of dates instead of a series of numbers, check my comments here:


SQL Optimisation :: Convert Primary Keys to Clustered Indexes

We recently spotted that one of the systems we use did not make use of clustered indexes on any tables out of the box. As a result performance was not as good as it could have been. The below script allows for an easy win optimisation by finding all tables which do not include a clustered index, and converting the table’s primary key to be a clustered index.

In a future post I’ll put up more details on what clustered indexes are, why you should always (pretty much) use them and other useful info for anyone playing with databases.

--This script is designed for MS SQL Server
use DbNameToOptimise

--disable all constraints on all tables (to avoid these causing errors when altering the indexes)
sp_msforeachtable 'alter table ? nocheck constraint all'
declare @sqls table(object_id bigint, sort int, sql nvarchar(max))
insert @sqls
select t.object_id, ic.key_ordinal, case when ic.key_ordinal=1 then  'CREATE UNIQUE CLUSTERED INDEX [' + + '] ON [' + + ']([' else ',[' end + + case when ic.key_ordinal=icagg.maxko then ']) WITH DROP_EXISTING' else ']' end sql
from sys.tables t
inner join sys.indexes i on t.object_id = i.object_id
inner join sys.index_columns ic on i.object_id=ic.object_id and  i.index_id = ic.index_id
inner join sys.columns c on ic.object_id = c.object_id and ic.column_id = c.column_id
inner join (
      select object_id, index_id, MAX(key_ordinal) maxko from sys.index_columns group by object_id,index_id
) icagg on i.object_id = icagg.object_id and i.index_id = icagg.index_id
where t.is_ms_shipped=0
and i.is_primary_key=1
and not exists (
      --ignore tables which already have a clustered index
      select 1
      from sys.indexes i2
      where t.object_id = i2.object_id
      and i2.type = 1
order by,, ic.key_ordinal
declare @objid bigint
, @sql nvarchar(max)
while exists (select top 1 1 from @sqls)
      set @sql=''
      select top 1 @objid=object_id from @sqls
      select @sql = @sql + sql from @sqls where object_id=@objid order by sort
      delete from @sqls where object_id = @objid
      exec (@sql)

--reenable constraints to leave the db as we found it (aside from the fix)
sp_msforeachtable 'alter table ? check constraint all'


BizTalk ConnectionString

Filed under: BizTalk, Ideas, Microsoft, Technology — Tags: , , , , , — Developer42 @ 19:24

When using BizTalk, there’s often one or two databases you’ll need to access regularly. Rather than hard coding these in parameters of the database methods, a potential solution is to create a functoid which returns the required connection string. This gives you the advantage that should you need to change your connection string, changing it in your functoid will simultaneously update everywhere using that connection string. Of course, once you’ve got one connection string to your configuration database, you can use simple names to access your other databases, since these names can be stored in your configuration database along with the relevant connection strings, making them even easier to maintain.

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