Im trying to load a CSV file from Amazon S3 into an Amazon Aurora MySQL table using the LOAD DATA FROM S3 statement.

You've encountered a common challenge when importing CSV data into Aurora MySQL, especially when dealing with empty values for numeric fields. Your solution of using '\N' to represent NULL values is indeed a good approach and is widely recognized in MySQL and Aurora MySQL.

To address your questions:

1. Using '\N' is a standard and recommended way to represent NULL values when importing CSV files into Aurora MySQL. This convention is recognized by MySQL and Aurora MySQL as a NULL indicator, especially when using LOAD DATA operations.

2. This behavior is documented in MySQL documentation, which Aurora MySQL follows closely. The '\N' (or '\N' when escaped) is treated as a NULL value by default during LOAD DATA operations.

3. While NULLIF() can work in some contexts, it's not always reliable for LOAD DATA operations, especially with empty strings. The issue you encountered with empty quotes ("") is a known quirk in how LOAD DATA processes fields.

Your approach of replacing empty numeric values with '\N' in the CSV file before import is a robust solution. It ensures that Aurora MySQL correctly interprets these values as NULL without requiring additional conversion logic in the LOAD DATA statement.

If you need to handle this at the database level rather than modifying the source CSV, you can use a combination of the NULL AS and SET clauses in your LOAD DATA statement. For example:

LOAD DATA FROM S3 's3://your-bucket/your-file.csv'
INTO TABLE your_table
FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"'
(column1, @var1, column2, @var2)
SET 
  column1 = NULLIF(@var1, ''),
  column2 = NULLIF(@var2, '');

This approach allows you to specify how empty fields should be treated, potentially avoiding the need to modify the source CSV.

Remember that when using LOAD DATA FROM S3 in Aurora MySQL, you need to ensure that the necessary IAM permissions are set up correctly to allow access to the S3 bucket.

In summary, while using '\N' in your CSV is a reliable method, you have options to handle this at both the data preparation stage and during the import process itself. The choice depends on your specific workflow and requirements.
Sources
Import CSV file in S3 into Aurora MySql | AWS re:Post
Loading data into an Amazon Aurora MySQL DB cluster from text files in an Amazon S3 bucket - Amazon Aurora

Hi,

Thank you so much for asking your question.

1. \N is indeed the official and recommended way to represent NULL values when importing CSV files into MySQL (and by extension, Aurora MySQL). The documentation explicitly states: "For the default FIELDS and LINES values, NULL is written as a field value of \N for output, and a field value of \N is read as NULL for input (assuming that the ESCAPED BY character is )."
2. This behavior is documented in the MySQL documentation in the "Handling of NULL values" section: https://dev.mysql.com/doc/refman/8.0/en/load-data.html

I hope this might help.