Sql-server – How I develop Union Report Views for Multiple Single Tenant Databases

data-warehousedynamic-sqlsql serversql-server-2016view

We have a database for each customer, over 20+ databases. All database schemas are the same. Now we want to create a Consolidated Reporting View for All Databases, for total database analysis. How would I dynamically generate views for tables in the database, which combine the data? The databases reside on the same server instance.

Many db professionals prefer single tenant databases.

Single Tenant Database Discussion

Best Answer

Code provided below: CustomerTemplateDb contains all the tables for single tenant database.

It will list other single tenant databases around it, and create one consolidated view in reporting database.

(Feel free to code review, or make modifications as needed. Works on my end)

declare @DatabaseTemplate nvarchar(max) = 'CustomerTemplate'
declare @DatabaseDestination nvarchar(max) = 'ReportingDb'
declare @TableSchema nvarchar(max)
declare @TableName nvarchar(max)

declare @DatabaseCurrent nvarchar(max)
declare @DatabaseCounter int = 1

declare @TableListGenerateCode nvarchar(max) = ''
declare @TableCounter int = 1

declare @DropView nvarchar(255) = ''

declare @TableSelectFromCurrentDatabaseCode nvarchar(max) = ''
declare @TableSelectFromAllDatabaseCode nvarchar(max) = ''

declare @ColumnSelectFromCurrentTableCode nvarchar(max) = ''



IF OBJECT_ID('tempdb..#DatabaseList') IS NOT NULL drop table #DatabaseList
create table #DatabaseList (DatabaseId int identity(1,1), DatabaseName varchar(255))


IF OBJECT_ID('tempdb..#TableList') IS NOT NULL drop table #TableList
create table #TableList (TableId int identity(1,1), TableSchema varchar(255), TableName varchar(255))

IF OBJECT_ID('tempdb..#ColumnList') IS NOT NULL drop table #ColumnList
create table #ColumnList (ColumnId int identity(1,1), ColumnName varchar(255))


insert into #DatabaseList (databasename)
select db.name  
from sys.databases db
where 
database_id > 4 
and db_Name(database_id) <> @DatabaseTemplate and db_Name(database_id) <> 'reportingdb' and db_Name(database_id) <> 'electronics' and db_Name(database_id) <> 'mytestdb'
and state = 0;

set @TableListGenerateCode=
'
Insert into #TableList (TableSchema, TableName)
SELECT TABLE_SCHEMA, TABLE_NAME
FROM ' + @DatabaseTemplate + '.INFORMATION_SCHEMA.TABLES
WHERE TABLE_TYPE = ''BASE TABLE'' AND table_catalog = ' + '''' + @DatabaseTemplate + ''''

exec (@TableListGenerateCode)



while @TableCounter <= (select count(*) from #TableList) 
begin

    set @TableSchema = (select TableSchema from #TableList where Tableid = @TableCounter)
    set @TableName = (select TableName from #TableList where Tableid = @TableCounter)
    set @DatabaseCounter = 1


    while @DatabaseCounter <= (select count(*) from #DatabaseList)
    begin

        set @DatabaseCurrent = (select DatabaseName from #DatabaseList where DatabaseId = @DatabaseCounter)

        truncate table #ColumnList
        set @ColumnSelectFromCurrentTableCode = 'insert into #ColumnList   select STUFF((
            SELECT '', 
        '' + QUOTENAME(c.name) 
            FROM ' + @DatabaseCurrent + '.sys.columns c where c.object_id = object_id(''' +  @DatabaseCurrent + '.' + @TableSchema + '.' + @Tablename +''')
            FOR XML PATH(''''), TYPE).value(''.'',''nvarchar(max)''),1,2,'''')'

        exec (@ColumnSelectFromCurrentTableCode)

        set @TableSelectFromCurrentDatabaseCode = 
    '
    UNION ALL 

    SELECT ' + (select top 1 ColumnName from #ColumnList) +
            ' 
    FROM ' + @DatabaseCurrent + '.' + @TableSchema + '.' +  @Tablename + CHAR(13)+CHAR(10) + '
            '
        set @TableSelectFromAllDatabaseCode = @TableSelectFromCurrentDatabaseCode + @TableSelectFromAllDatabaseCode 

        set @DatabaseCounter = @DatabaseCounter + 1

    end

        set @TableSelectFromAllDatabaseCode = N' EXEC ' + @DatabaseDestination + '.sys.sp_executesql ' + 'N''Create View ' + @Tablename + 'Vw as 
        ' + RIGHT(@TableSelectFromAllDatabaseCode, LEN(@TableSelectFromAllDatabaseCode) - 12)+''''


        PRINT @TableSelectFromAllDatabaseCode

        --PRINT ('Create View ' + @Tablename + 'Vw as 
        --' + RIGHT(@TableSelectFromAllDatabaseCode, LEN(@TableSelectFromAllDatabaseCode) - 13)+'''');

        set @DropView = N' EXEC ' + @DatabaseDestination + '.sys.sp_executesql ' + 'N''IF OBJECT_ID(''''' + @TableName + 'Vw'''', ''''V'''') IS NOT NULL   DROP VIEW ' + @Tablename + 'Vw' + ''''

        exec (@DropView)
        exec (@TableSelectFromAllDatabaseCode)
        set @TableCounter = @TableCounter + 1

        set @DropView = ''
        set @TableSelectFromCurrentDatabaseCode = ''
        set @TableSelectFromAllDatabaseCode = ''


end
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