Importing data into a live table isn't generally good practice unless it's a repetitive process and problems have been sorted on previous imports.
Instead, import into a staging table, which should be a full or partial copy (columnwise) of the target table with no constraints. Check the new data once it's in the staging table, then import into the live table. Then purge or delete the staging table. Much safer, much easier to check.
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Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden