I have a stored procedure that dynamically generates MERGE TSQL statements to handle SCD Type 1 updates between the given Dimension / Staging table dump.
Here is the T-SQL code (modified from the original code by Alex Whittles):
USE [OPPY_DWUSD]
GO
ALTER PROCEDURE [dbo].[GenerateMerge]
/***************************************************************
* *
* Script for use with blog post *
* "Automating T-SQL Merge to load Dimensions (SCD)" *
* http://www.purplefrogsystems.com/blog/2012/04/automating-t-sql-merge-to-load-dimensions-scd
* *
* Posted: 6th April 2012 *
* *
* By: Alex Whittles - Purple Frog Business Intelligence *
* www.PurpleFrogSystems.com *
* *
* All code samples are provided “AS IS” without warranty of *
* any kind, either express or implied, including but not *
* limited to the implied warranties of merchantability *
* and/or fitness for a particular purpose. *
* *
***************************************************************/
@Dimension varchar(50),
@Schema varchar(50),
@ETLTable varchar(50),
@ETLSchema varchar(50),
@Execute bit=0 --Should the resulting merge be returned or executed
AS
BEGIN
SET NOCOUNT ON;
--Create Carriage return variable to format the resulting query
DECLARE @crlf char(2)
SET @crlf = CHAR(13)
--Find out which Audit fields are used
DECLARE @UseIsInferred bit
DECLARE @UseFirstCreated bit
DECLARE @UseValidTo bit
DECLARE @UseIsRowCurrent bit
DECLARE @UseLastUpdated bit
SET @UseIsInferred = ISNULL((SELECT MAX(1)
FROM sys.columns c
INNER JOIN sys.tables t on c.object_id = t.object_id
INNER JOIN sys.schemas s ON t.schema_id = s.schema_id
WHERE s.name = @Schema
AND t.name = @Dimension
AND c.name = 'IsInferred'
),0)
SET @UseFirstCreated= ISNULL((SELECT MAX(1)
FROM sys.columns c
INNER JOIN sys.tables t on c.object_id = t.object_id
INNER JOIN sys.schemas s ON t.schema_id = s.schema_id
WHERE s.name = @Schema
AND t.name = @Dimension
AND c.name = 'FirstCreated'
),0)
SET @UseValidTo = ISNULL((SELECT MAX(1)
FROM sys.columns c
INNER JOIN sys.tables t on c.object_id = t.object_id
INNER JOIN sys.schemas s ON t.schema_id = s.schema_id
WHERE s.name = @Schema
AND t.name = @Dimension
AND c.name = 'ValidTo'
),0)
SET @UseIsRowCurrent = ISNULL((SELECT MAX(1)
FROM sys.columns c
INNER JOIN sys.tables t on c.object_id = t.object_id
INNER JOIN sys.schemas s ON t.schema_id = s.schema_id
WHERE s.name = @Schema
AND t.name = @Dimension
AND c.name = 'IsRowCurrent'
),0)
SET @UseLastUpdated = ISNULL((SELECT MAX(1)
FROM sys.columns c
INNER JOIN sys.tables t on c.object_id = t.object_id
INNER JOIN sys.schemas s ON t.schema_id = s.schema_id
WHERE s.name = @Schema
AND t.name = @Dimension
AND c.name = 'LastUpdated'
),0)
--Identify the business key column(s)
--Also define what the null replacement should be
DECLARE myCurBK Cursor FOR
SELECT c.name
, CASE WHEN ty.name IN ('text', 'ntext', 'varchar', 'char', 'nvarchar', 'nchar') THEN ''''''
WHEN ty.name IN ('tinyint', 'smallint', 'int', 'real', 'money', 'float', 'bit', 'decimal', 'numeric','smallmoney','bigint') THEN '0'
WHEN ty.name IN ('date', 'datetime') THEN '''19000101'''
ELSE 'NULL' END AS NullRep
FROM sys.columns c
INNER JOIN sys.tables t on c.object_id = t.object_id
INNER JOIN sys.schemas s ON t.schema_id = s.schema_id
INNER JOIN sys.types ty ON c.user_type_id = ty.user_type_id
INNER JOIN sys.extended_properties ep
ON t.object_id=ep.major_id
AND c.column_id=ep.minor_id
AND ep.class=1
AND ep.name='SCD'
WHERE s.name = @Schema
AND t.name = @Dimension
AND ep.value = 'BK'
ORDER BY c.column_id
--Identify all fields to be merged (Exclude Type 0)
DECLARE myCurType1 Cursor
FOR SELECT c.name
, CASE WHEN ty.name IN ('text', 'ntext', 'varchar', 'char', 'nvarchar', 'nchar') THEN ''''''
WHEN ty.name IN ('tinyint', 'smallint', 'int', 'real', 'money', 'float', 'bit', 'decimal', 'numeric','smallmoney','bigint') THEN '0'
WHEN ty.name IN ('date', 'datetime') THEN '''19000101'''
ELSE 'NULL' END AS NullRep
FROM sys.columns c
INNER JOIN sys.tables t on c.object_id = t.object_id
INNER JOIN sys.schemas s ON t.schema_id = s.schema_id
INNER JOIN sys.types ty ON c.user_type_id = ty.user_type_id
LEFT JOIN sys.extended_properties ep
ON t.object_id=ep.major_id
AND c.column_id=ep.minor_id
AND ep.class=1
AND ep.name='SCD'
WHERE s.name = @Schema
AND t.name = @Dimension
AND c.is_identity=0
AND ISNULL(ep.value,'1') NOT IN ('0', 'Audit', 'BK')
ORDER BY c.column_id ASC
--Identify all fields for insert
DECLARE myCurAll Cursor
FOR SELECT c.name
, CASE WHEN ty.name IN ('text', 'ntext', 'varchar', 'char', 'nvarchar', 'nchar') THEN ''''''
WHEN ty.name IN ('tinyint', 'smallint', 'int', 'real', 'money', 'float', 'bit', 'decimal', 'numeric','smallmoney','bigint') THEN '0'
WHEN ty.name IN ('date', 'datetime') THEN '''19000101'''
ELSE 'NULL' END AS NullRep
FROM sys.columns c
INNER JOIN sys.tables t on c.object_id = t.object_id
INNER JOIN sys.schemas s ON t.schema_id = s.schema_id
INNER JOIN sys.types ty ON c.user_type_id = ty.user_type_id
WHERE s.name = @Schema
AND t.name = @Dimension
AND c.name NOT IN ('LastUpdated', 'IsInferred', 'FirstCreated', 'ValidTo', 'IsRowCurrent')
AND c.is_identity=0
ORDER BY c.column_id ASC
DECLARE @Field varchar(255)
DECLARE @NullRep varchar(20)
DECLARE @SQL varchar(max)
DECLARE @SQL2 varchar(max)
DECLARE @SQL3 varchar(max)
--Now start building up the dynamic SQL
SET @SQL ='MERGE [' + @Schema + '].[' + @Dimension + '] AS Target'
SET @SQL = @SQL + @crlf + 'USING [' + @ETLSchema + '].[' + @ETLTable + '] AS Source'
OPEN myCurBK
FETCH NEXT FROM myCurBK INTO @Field, @NullRep
IF (@@FETCH_STATUS>=0)
BEGIN
SET @SQL = @SQL + @crlf + ' ON Target.' + '[' + @Field + ']' + ' = Source.' + '[' + @Field + ']'
FETCH NEXT FROM myCurBK INTO @Field, @NullRep
END
WHILE (@@FETCH_STATUS<>-1)
BEGIN
IF (@@FETCH_STATUS<>-2)
SET @SQL = @SQL + @crlf + ' AND Target.' + '[' + @Field + ']' + ' = Source.' + '[' + @Field + ']'
FETCH NEXT FROM myCurBK INTO @Field, @NullRep
END
CLOSE myCurBK
IF @UseIsRowCurrent>0 SET @SQL = @SQL + @crlf + ' AND Target.IsRowCurrent=1'
SET @SQL = @SQL + @crlf + ' WHEN MATCHED'
OPEN myCurType1
FETCH NEXT FROM myCurType1 INTO @Field, @NullRep
IF (@@FETCH_STATUS>=0)
BEGIN
SET @SQL = @SQL + @crlf + ' AND (ISNULL(Target.' + '[' + @Field + ']' + ',' + @NullRep + ') <> ISNULL(Source.' + '[' + @Field + ']' + ',' + @NullRep + ')'
FETCH NEXT FROM myCurType1 INTO @Field, @NullRep
END
WHILE (@@FETCH_STATUS<>-1)
BEGIN
IF (@@FETCH_STATUS<>-2)
SET @SQL = @SQL + @crlf + ' OR ISNULL(Target.' + '[' + @Field + ']' + ',' + @NullRep + ') <> ISNULL(Source.' + '[' + @Field + ']' + ',' + @NullRep + ')'
FETCH NEXT FROM myCurType1 INTO @Field, @NullRep
END
CLOSE myCurType1
SET @SQL = @SQL + @crlf + ' )'
SET @SQL2 = ' THEN UPDATE SET'
OPEN myCurType1
FETCH NEXT FROM myCurType1 INTO @Field, @NullRep
IF (@@FETCH_STATUS>=0)
BEGIN
SET @SQL2 = @SQL2 + @crlf + ' ' + '[' + @Field + ']' + ' = Source.' + '[' + @Field + ']'
FETCH NEXT FROM myCurType1 INTO @Field, @NullRep
END
WHILE (@@FETCH_STATUS<>-1)
BEGIN
IF (@@FETCH_STATUS<>-2)
SET @SQL2 = @SQL2 + @crlf + ' ,' + '[' + @Field + ']' + ' = Source.' + '[' + @Field + ']'
FETCH NEXT FROM myCurType1 INTO @Field, @NullRep
END
CLOSE myCurType1
IF @UseLastUpdated>0 SET @SQL2 = @SQL2 + @crlf + ' ,LastUpdated = GetDate()'
SET @SQL3 = ' WHEN NOT MATCHED THEN'
SET @SQL3 = @SQL3 + @crlf + ' INSERT ('
OPEN myCurAll
FETCH NEXT FROM myCurAll INTO @Field, @NullRep
IF (@@FETCH_STATUS>=0)
BEGIN
SET @SQL3 = @SQL3 + @crlf + ' ' + '[' + @Field + ']'
FETCH NEXT FROM myCurAll INTO @Field, @NullRep
END
WHILE (@@FETCH_STATUS<>-1)
BEGIN
IF (@@FETCH_STATUS<>-2)
SET @SQL3 = @SQL3 + @crlf + ' ,' + '[' + @Field + ']'
FETCH NEXT FROM myCurAll INTO @Field, @NullRep
END
CLOSE myCurAll
IF @UseIsInferred>0 SET @SQL3 = @SQL3 + @crlf + ' ,IsInferred'
IF @UseFirstCreated>0 SET @SQL3 = @SQL3 + @crlf + ' ,FirstCreated'
IF @UseValidTo>0 SET @SQL3 = @SQL3 + @crlf + ' ,ValidTo'
IF @UseIsRowCurrent>0 SET @SQL3 = @SQL3 + @crlf + ' ,IsRowCurrent'
IF @UseLastUpdated>0 SET @SQL3 = @SQL3 + @crlf + ' ,LastUpdated'
SET @SQL3 = @SQL3 + @crlf + ' ) VALUES ('
OPEN myCurAll
FETCH NEXT FROM myCurAll INTO @Field, @NullRep
IF (@@FETCH_STATUS>=0)
BEGIN
SET @SQL3 = @SQL3 + @crlf + ' Source.' + '[' + @Field + ']'
FETCH NEXT FROM myCurAll INTO @Field, @NullRep
END
WHILE (@@FETCH_STATUS<>-1)
BEGIN
IF (@@FETCH_STATUS<>-2)
SET @SQL3 = @SQL3 + @crlf + ' ,Source.' + '[' + @Field + ']'
FETCH NEXT FROM myCurAll INTO @Field, @NullRep
END
CLOSE myCurAll
IF @UseIsInferred>0 SET @SQL3 = @SQL3 + @crlf + ' ,0'
IF @UseFirstCreated>0 SET @SQL3 = @SQL3 + @crlf + ' ,GetDate()'
IF @UseValidTo>0 SET @SQL3 = @SQL3 + @crlf + ' ,NULL'
IF @UseIsRowCurrent>0 SET @SQL3 = @SQL3 + @crlf + ' ,1'
IF @UseLastUpdated>0 SET @SQL3 = @SQL3 + @crlf + ' ,GetDate()'
SET @SQL3 = @SQL3 + @crlf + ' );'
--clean up
DEALLOCATE myCurType1
DEALLOCATE myCurAll
DEALLOCATE myCurBK
IF @Execute = 1
BEGIN
EXEC(@SQL + @SQL2 + @SQL3)
END
ELSE
BEGIN
PRINT @SQL
PRINT @SQL2
PRINT @SQL3
END
END
In the stored procedure above, when I pass in the variables, it produces this code:
MERGE [DIM].[COMPANY] AS Target
USING [DBO].[DWUSD_LIVE] AS Source
ON Target.[comp] = Source.[comp]
WHEN MATCHED
AND (ISNULL(Target.[comp name],'') <> ISNULL(Source.[comp name],'')
OR ISNULL(Target.[comp description],'') <> ISNULL(Source.[comp description],'')
)
THEN UPDATE SET
[comp name] = Source.[comp name]
,[comp description] = Source.[comp description]
,LastUpdated = GetDate()
WHEN NOT MATCHED THEN
INSERT (
[comp]
,[comp name]
,[comp description]
,FirstCreated
,LastUpdated
) VALUES (
Source.[comp]
,Source.[comp name]
,Source.[comp description]
,GetDate()
,GetDate()
);
What I need to be able to do is add a DISTINCT SELECT subquery at the beginning…
MERGE [dim].[Company] AS Target
USING (
SELECT DISTINCT
[COMP NAME],
[COMP DESCRIPTION],
[COMP]
FROM [dbo].[DWUSD_LIVE]
) AS Source
So that when it looks at the source (staging table) it does a SELECT DISTINCT on the same columns found in the dimension but not including the audit columns (FirstCreated / LastUpdated).
My staging table has duplicate records, thus I only need to SELECT DISTINCT otherwise I end up with multiple records in my dimension.
It looks like you pass the table you want to use as a source to the stored procedure in these variables:
Those same variables are used in defining the source:
I believe, as long as you have the same columns you would need from the actual source table, you can take the distinct query you want to use, create a view with it and pass that table to the stored proc.
The exec statement would look something like:
Also, you won’t have to modify the stored proc, which looks like it may be called by other processes and if you have this same situation with other tables, you can apply a similar solution.