I’m getting the below error while trying to ADD CONSTRAINT in Azure DataWarehouse

Functions in Azure DW don't support select statements that access tables like in your use case, see CREATE FUNCTION (SQL Data Warehouse):

function_body
Specifies that a series of Transact-SQL statements, which do not reference database data (tables or views), define the value of the function.

Could you double check that function is created in DW?

Polybase is powerful but not really that sophisticated so will not be able to deal with this weird format. You have three options as I see it:

1. Correct the file format at source. Instead of having weird mix of fixed-width and delimited file format, use a standard file format, such as .csv. This format you have where the column delimiter is either carriage return or comma I think is genuinely strange. Are there any tools that can read this easily? Is this a common format where you work?
2. Import the file specifying one of the delimiters into one row, then shred it based on the other delimiter. I started trying this with your sample data but did not get very far. Do different rows really have different numbers of columns? In your sample data, row 1 has 24 columns and row 2 has 17 columns. Please provide a small sample file eg via gist that accurately represents your data.
3. Write a highly customised import routine. The point of using standard data interchange formats like csv, tab-delimted, pipe-delimited, XML, JSON etc is that you should not have to write a highly custom routine every time you want to import some data. However, this could be an option, if you cannot change your file at source, or import it in stages. I've been working with Azure Data Lake Analytics (ADLA) and U-SQL recently, and that might be able to do this.

Please try and answer my questions above and provide a sample file and I will try and help.