MERGE Command in SQL Server - sql

Question

I have been using the statement
insert into target
select * from source
where [set of conditions] for a while.
Recently found this MERGE command that will be more effective to use for my purpose so that I can change the above statement to
MERGE target
USING source ON [my condtion]
WHEN NOT MATCHED BY TARGET
THEN INSERT VALUES (source.col1, source.col2, source.col3)
But the problem for me is lets say if I have 20+ columns in my source table I have to list all of them, I need a way to specify it to insert source.* . Is there a way ? I'm new to SQL. Appreciate your help.
Thanks in advance :)

Answer 1

Me too; I hate typing column names.
I normally build the Merge statement in dynamic SQL.
I have a function that takes a table name as a parameter, and returns a string containing all column names formatted properly with Table Name prefix, [] brackets and comma, as in S.Col1, S.Col2, S.Col3
I could also tell you that I build a temp table with the required columns, and pass the temp table to my function, because some times you don't want a list of all columns. But that would probably be a confusing wooble, obscuring the important bits;
Use dynamic sql
Use a function to create csv list of columns.

Answer 2

Everything that I have read regarding the MERGE statement says that you need to specify the columns for your INSERT statement. If you are looking for a quick way to get the INSERT statment, you can right mouse click the table in SSMS and select Script Table As->INSERT To->Clipboard. You can then paste this into your query and alter just the VALUES part.
Merge statement

Answer 3

There's simply no advantage of using MERGE in this situation. Why overcomplicate? Stick to the KISS principle, for chrissake.
Anyways, here's the script:
declare
#targetTableName varchar(100) = 'target'
,#targetSchemaName varchar(20) = 'dbo'
,#sourceTableName varchar(100) = 'source'
,#sourceSchemaName varchar(20) = 'dbo2'
,#matchCondition varchar(50) = 't.id = s.id'
,#columns varchar(max)
set #columns = (select ','+quotename(c.name)
from sys.tables t
join sys.columns as c on t.object_id = c.object_id
join sys.schemas s on s.schema_id = t.schema_id
where t.name = #targetTableName and s.name = isnull(#targetSchemaName, s.name)
for xml path(''))
--a column name starts with a comma
declare #sql varchar(max) = '
merge #target t
using #source s on #matchCondition
when not matched then
insert (#columns)
values #sourceColumns'
set #sql =
replace(replace(replace(replace(replace(#sql
, '#matchCondition', #matchCondition)
--replace #columns with column list with the first comma removed
, '#columns', stuff(#columns, 1, 1, ''))
--replace #sourceColumns with column list with the 's.' prefix and comma removed
, '#sourceColumns', stuff(replace(#columns, ',', ',s.'),1,1,''))
, '#target', quotename(#targetSchemaName)+'.'+quotename(#targetTableName))
, '#source', quotename(#sourceSchemaName)+'.'+quotename(#sourceTableName))
print #sql
--exec(#sql)
And we'll get something like this:
merge [dbo].[target] t
using [dbo2].[source] s on t.id = s.id
when not matched then
insert ([column1], [column2], [column3], [column4])
values s.[column1], s.[column2], s.[column3], s.[column4]