How to Fill Table Data based on Condition in SQL Server - sql

Question

My Tables are defined like below:
UserData (ColA, ColB, ColC) - This table fills by .CSV file.
These column names are not fixed and number of Table Columns varies in different .CSV files depending on the customer giving the .CSV file.
UserDataDSU (ColD, ColE, ColF, ColG, ColH, ColI, ColJ)
Now, I have to fill UserDataDSU table with UserData table data like below.
If UserData(ColC) exists and it has data, then fill UserDataDSU(ColD) else set ColD as NULL
If UserData(ColA) exists and it has data, then fill UserDataDSU(ColE) else set ColE as NULL
If UserData(ColB) exists and it has data, then fill UserDataDSU(ColF) else set ColF as NULL
Of course, for all the remaining columns in UserDataDSU (like ColG, ColH, ColI, ColJ does not have data in its couter table - UserData, all those should be filled by NULLs.
Please remember that for some other .CSV file got from another customer DATA MAY EXISTS FOR SOME OR ALL OF THESE COLUMNS
Can anyone please suggest how to do this inside a Stored procedure.

Answer 1

TLDR
You can use sys.objects to generate a match the columns between tables based on your business logic and then use this mapping to create a dynamic INSERT sql script.
Below is the SQL script for all this
DECLARE #sql varchar(max) -- will be used for holding dynamic SQL script
-- this temp table will hold the mapping
CREATE TABLE #temp (DColName varchar(100), SColName varchar(100), OrderCol int)
--inserting mapping into temp table based on business logic
INSERT INTO #temp
SELECT
Dest.name,
Source.name,
Dest.object_id -- ordering criteria to generate accurate mapping in script
FROM
sys.columns Dest LEFT JOIN
(
SELECT
name,
CASE
WHEN name='ColC' THEN 'ColD'
WHEN name='ColA' THEN 'ColE'
WHEN name='ColB' THEN 'ColF'
ELSE name
END as Newname -- business logic for matching
FROM
sys.columns
WHERE
object_id IN (
SELECT object_id FROM sys.tables WHERE name ='UserData'
)
)source
ON Dest.Name=Source.NewName
WHERE
Dest.object_id IN (
SELECT object_id
FROM sys.tables
WHERE name ='UserDataDSU'
)
--create the dynamic SQL
SELECT #sql =
'INSERT INTO UserDataDSU ('+
--insert column list of destination table
STUFF((SELECT ','+ Dcolname FROM #temp WHERE Scolname IS NOT NULL ORDER BY OrderCol ASC FOR XML PATH('')),1,1,'') +
') SELECT '+
--insert column list of source table
STUFF((SELECT ','+ Scolname FROM #temp ORDER BY OrderCol ASC FOR XML PATH('')),1,1,'') +
' FROM UserData'
-- execute the dynamic SQL
EXEC(#sql)
-- now drop the temp table
DROP TABLE #temp
Please note that I tested this and this worked for me.
CREATE INSERT table scripts used are below
create table UserData (ColA varchar(100), ColB varchar(100), ColC varchar(100));
insert into UserData values ('A1','B1','C1'),('A2','B2','C2');
create table UserDataDSU (ColD varchar(100), ColE varchar(100), ColF varchar(100), ColG varchar(100), ColH varchar(100), ColI varchar(100), ColJ varchar(100));