Here is a very useful command using which you can merge multiple CSV into one large file. Follow the steps:

cmd_merge_csv

Step I: Copy all files to merge in one folder.

Step II: Start command Prompt. Goto to the folder using CD command.

Step III: once are in the folder, then fire the command: E:\csv_files>copy *.csv complete_records.csv

Stpe IV: Press Enter. And Done