将Excel表转换为C＃中的SQL表-将Excel中的多个列映射到SQL中的单个列

Question

I am trying to upload individual ListObject tables in excel to SQL tables in a database.

I have already wrote code that simply generates an SQL query string and executes - this works but it's not easily maintainable.

So I found this technique: https://stackoverflow.com/a/11268550/1610402

This allows me to fill a data table and bulk insert that into SQL; with column mapping capabilities if they are required.

However my table structure in Excel differs more than simply column 'names' to avoid redundant data.

Therefore I need to map columns from Excel (example):

Column1    Column2   '2015'  '2016'  '2017'  '2018'  '2019'  '2020'
1          1          0.1     0.2     0.3     0.35    0.375   0.4
1          2          0.1     0.2     0.3     0.35    0.375   0.4

To columns in SQL, like the following:

Column1    Column2    Year    Value
1          1          2015    0.1
1          1          2016    0.2
1          1          2017    0.3
1          1          2018    0.35
1          1          2019    0.375
1          1          2020    0.4
1          2          2015    0.1
1          2          2016    0.2
1          2          2017    0.3
1          2          2018    0.35
1          2          2019    0.375
1          2          2020    0.4

Is there a better way of doing this in C# .Net or should I stick with my nested for loop and string builder?

Answer 1

The concept of what you want is called 'unpivoting'. Whether you do this in C# or is not of importance, since you can simply load the first data in SQL-Server and unpivot this data by

SELECT IDENTITY(int,1,1) as RowId, Column1, Column2, [Year], [Value]
INTO newTable
FROM (
   SELECT Column1,Column2,[2015],[2016],[2017],[2018],[2019],[2020] FROM oldTable
) as source
UNPIVOT
(
   [Value] for [Year] in [2015],[2016],[2017],[2018],[2019],[2020]
) as target

The square brackets are required to make these strings appear as column names in stead of numbers or reserved words.