امیر میرکمالی

declare @NewCollation varchar(255) ,@Stmt nvarchar(4000) ,@DBName sysname set @NewCollation = 'SQL_Latin1_General_CP1256_CI_AS' -- change this to the collation that you need set @DBName = DB_NAME() declare @CName varchar(255) ,@TName sysname ,@OName sysname ,@Sql varchar(8000) ,@Size int ,@Status tinyint ,@Colorder int declare curcolumns cursor read_only forward_only local for select QUOTENAME(C.Name) ,T.Name ,QUOTENAME(U.Name) + '.' +QUOTENAME(O.Name) ,C.Prec ,C.isnullable ,C.colorder from syscolumns C inner join systypes T on C.xtype=T.xtype inner join sysobjects O on C.ID=O.ID inner join sysusers u on O.uid = u.uid where T.Name in ('varchar', 'char', 'text', 'nchar', 'nvarchar', 'ntext') and O.xtype in ('U') and C.collation != @NewCollation and objectProperty(O.ID, 'ismsshipped')=0 order by 3, 1 open curcolumns SET XACT_ABORT ON begin tran fetch curcolumns into @CName, @TName, @OName, @Size, @Status, @Colorder while @@FETCH_STATUS =0 begin set @Sql='ALTER TABLE '+@OName+' ALTER COLUMN '+@CName+' '+@TName+ isnull ('(' +CASE @Size WHEN -1 then 'max' else convert(varchar,@Size) end+')', '') +' COLLATE '+ @NewCollation +' '+case when @Status=1 then 'NULL' else 'NOT NULL' end --exec(@Sql) -- change this to print if you need only the script, not the action PRINT @Sql fetch curcolumns into @CName, @TName, @OName, @Size, @Status, @Colorder end close curcolumns deallocate curcolumns commit tran

public int GetOrdinal(string tableName, string name) { DataView schema = GetSchemaTable().DefaultView; schema.RowFilter = String.Format("BaseTableName='{0}' AND ColumnName='{1}'", tableName, name); if (schema.Count > 0) return Convert.ToInt32(schema[0]["ColumnOrdinal"]); else throw new IndexOutOfRangeException(); }

Sometimes the schema of a replicated table needs altering. There are many reasons this might be the case eg possibly the datatype has been incorrectly chosen, or a default is missing, or we want to rename a column. Attempting to change the table schema directly will result in the error

"Cannot alter/drop the table 'tablename' because it is being published for replication".

So, how to change an existing column without breaking replication? Consider if we wanted to make the following schema change:

The method we choose depends in part on the replication type and size of the table, but there are 2 main options:

(a) altering the subscriptions

  exec sp_dropsubscription   @publication =  'tTestFNames' 
     ,  @article =  'tEmployees' 
     ,  @subscriber =  'RSCOMPUTER'
     ,  @destination_db =  'testrep' 
  

  exec sp_droparticle  @publication =  'tTestFNames'
     ,  @article =  'tEmployees'
  

  alter table tEmployees alter column Forename varchar(100) null
  

  exec sp_addarticle  @publication =  'tTestFNames' 
     ,  @article =  'tEmployees' 
     ,  @source_table =  'tEmployees' 
  

  exec sp_addsubscription  @publication =  'tTestFNames'
     ,  @article =  'tEmployees'
     ,  @subscriber =  'RSCOMPUTER' 
     ,  @destination_db =  'testrep'

For snapshot replication this is the obvious choice. We drop the subscription to this article, drop the article, then change the table. Afterwards the process is reversed. The next time the snapshot agent is run, it'll pick up the new schema without any issues.

For transactional replication we may choose to proceed using the script above. However, we must be more careful in this case. By default, an insert, update or delete statement performed on the publisher is propagated to the subscriber in the form of a stored procedure call. By changing the column definition, we may need to change the related stored procedures on all the subscribers. Addition of a default would be fine, but changing the datatype itself as above would require the stored procedure arguments to be modified. For the example table above, these 3 procedures exist on the subscriber in the form:

sp_MSins_tEmployees,
sp_MSupd_tEmployees,
sp_MSdel_tEmployees.

They can be generated at the publisher using sp_scriptpublicationcustomprocs but this would of course require the system to be quiesced, i.e. during this (quick) change there shouldn't be any alterations made to the publisher's data and all the subscribers should be completely synchronized.

This is not ideal, and there is also a hidden problem here waiting to be discovered. Usually, when you add a new article to an existing publication in transactional replication, running the snapshot agent will create a snapshot of just the new article. In our case, it'll also create a snapshot of the 'tEmployees' table. So, to avoid all the issues and complications mentioned above, it's simplest to run the snapshot agent immediately after executing sp_addsubscription and then synchronize.

In merge replication, there is no possibility of dropping the subscription on a per article basis using the script above, as there is in transactional and snapshot replication. If we drop the subscription entirely including all other articles (sp_dropmergesubscription), then try to run sp_dropmergearticle there will be an error if the snapshot has already been run, so we have to set @forceinvalid_snapshot to 1, make the table change on the publisher then read the article and subscriptions and initialize which would necessitate a new snapshot generation of all articles in this publication. A nosync initialization is possible, but this can be extremely restrictive for future changes, and I'll leave that for another article.

(b) altering the table in-place

OK, in some cases the table is large and we don't want to run a new snapshot - either of the individual table (transactional) or of the whole publication (merge) - so there is an alternative method. We might use the built in stored procedures sp_repladdcolumn and sp_repldropcolumn to make the changes (note that these procedures limit the subscribers to be SQL Server 2000 only). Using these procedures we can add a dummy column to hold the data, remove the old column, add in the correct definition of the original column then transfer back the data. Now the script becomes:

  exec sp_repladdcolumn  @source_object =  'tEmployees'
     ,  @column =  'TempForename' 
     ,  @typetext =  'varchar(100) NULL' 
     ,  @publication_to_add =  'tTestFNames' 
  

  update tEmployees set TempForename = Forename
  

  exec sp_repldropcolumn  @source_object =  'tEmployees' 
     ,  @column =  'Forename' 
  

  exec sp_repladdcolumn  @source_object =  'tEmployees'
     ,  @column =  'Forename' 
     ,  @typetext =  'varchar(100) NULL' 
     ,  @publication_to_add =  'tTestFNames' 
  

  update tEmployees set Forename = TempForename
  

  exec sp_repldropcolumn  @source_object =  'tEmployees' 
     ,  @column =  'TempForename'

Although the above script can be used for transactional replication or merge replication, the internal methodology is different due to the differing nature of these 2 techniques. For merge replication, details of the rows updated are kept in MSmerge_contents, and if a particular row has been changed once or a hundred times, there will still only be one entry in this system table, while in transactional replication, 100 updates to a row is propagated as 100 subscriber updates. This means merge has an advantage over transactional because we need to perform 2 updates to each row to make the schema change.

You can find the main article in: http://www.sqlservercentral.com/articles/Replication/alteringacolumnonareplicatedtable/1666/

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public DataView GetTopDataViewRows(DataView source, int count) { DataTable output = source.Table.Clone(); for (int i = 0; i < count; i++) { if (i >= source.Count) break; output.ImportRow(source[i].Row); } return new DataView(output, source.RowFilter, source.Sort, source.RowStateFilter); }

CREATE TABLE #TmpWho (spid INT, ecid INT, status VARCHAR(150), loginame VARCHAR(150), hostname VARCHAR(150), blk INT, dbname VARCHAR(150), cmd VARCHAR(150)) INSERT INTO #TmpWho EXEC sp_who DECLARE @spid INT DECLARE @getspid CURSOR SET @getspid = CURSOR FOR SELECT spid FROM #TmpWho WHERE dbname = 'YOURDBNAME' OPEN @getspid FETCH NEXT FROM @getspid INTO @spid WHILE @@FETCH_STATUS = 0 BEGIN KILL @spid --SELECT @spid works fine here FETCH NEXT FROM @getspid INTO @spid END CLOSE @getspid DEALLOCATE @getspid DROP TABLE #TmpWho

DECLARE @tableCatalog VARCHAR (1024) , @tableSchema VARCHAR (1024), @tableName VARCHAR (1024), @tableType VARCHAR (1024) DECLARE cursorTemp CURSOR FOR SELECT * FROM INFORMATION_SCHEMA.TABLES OPEN cursorTemp FETCH cursorTemp INTO @tableCatalog, @tableSchema, @tableName, @tableType -- start the main processing loop. WHILE @@Fetch_Status = 0 BEGIN EXEC (' ALTER TABLE '+@tableName+' NOCHECK CONSTRAINT ALL;' + ' DELETE FROM '+ @tableName +';'+ ' ALTER TABLE '+@tableName+' CHECK CONSTRAINT ALL ') FETCH cursorTemp INTO @tableCatalog, @tableSchema, @tableName, @tableType END CLOSE cursorTemp DEALLOCATE cursorTemp