Import CSV to Database

I am Importing my CSV file to Database, but when i import the same CSV with extra records then those records are not reflects in Database.

Example,

Suppose i have CSV having records 1,2,3,4,5......and now i am import the CSV having records 1,2,3,4,5,6,7,8......

then it does not reflects 6,7,8 records in Database.

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