El problema es cómo MySQL interpreta un campo vacío frente a un campo faltante . De los documentos para LOAD DATA INFILE ...
En este caso, parece que MySQL lo considera vacío . Puedes ver esto desde show warnings .
mysql> show warnings;
+---------+------+------------------------------------------------------------+
| Level | Code | Message |
+---------+------+------------------------------------------------------------+
| Warning | 1265 | Data truncated for column 'customerReviewAverage' at row 2 |
| Warning | 1265 | Data truncated for column 'customerReviewAverage' at row 3 |
+---------+------+------------------------------------------------------------+
2 rows in set (0.00 sec)
Mientras que si eliminamos las comas finales, el campo falta ...
19658847,Glanzlichter - CD,,12.99,5.0
19658856,Glanzlichter - CD,,6.99
19658865,Glanzlichter - CD,,8.99
1965886,Beach Boys '69 - CASSETTE,,6.99,4.5
Luego, los datos se establecen en nulo.
mysql> show warnings;
+---------+------+--------------------------------------------+
| Level | Code | Message |
+---------+------+--------------------------------------------+
| Warning | 1261 | Row 2 doesn't contain data for all columns |
| Warning | 1261 | Row 3 doesn't contain data for all columns |
+---------+------+--------------------------------------------+
mysql> select * from products;
+----------+---------------------------+-------------+--------------+-----------------------+
| sku | name | description | regularPrice | customerReviewAverage |
+----------+---------------------------+-------------+--------------+-----------------------+
| 19658847 | Glanzlichter - CD | NULL | 12.99 | 5 |
| 19658856 | Glanzlichter - CD | NULL | 6.99 | NULL |
| 19658865 | Glanzlichter - CD | NULL | 8.99 | NULL |
| 1965886 | Beach Boys '69 - CASSETTE | NULL | 6.99 | 4.5 |
+----------+---------------------------+-------------+--------------+-----------------------+
4 rows in set (0.00 sec)
Hacer lo mismo para @customerReviewAverage como para @description funcionó para mí en MySQL 5.7.
LOAD DATA
LOCAL INFILE 'product.csv'
INTO TABLE Products
FIELDS TERMINATED BY ','
ENCLOSED BY '"'
LINES TERMINATED BY '\n'
(sku, name, @description, regularPrice, @customerReviewAverage)
SET description = IF(@description='',NULL,@description),
customerReviewAverage = IF(@customerReviewAverage='',NULL,@customerReviewAverage);
mysql> select * from products;
+----------+---------------------------+-------------+--------------+-----------------------+
| sku | name | description | regularPrice | customerReviewAverage |
+----------+---------------------------+-------------+--------------+-----------------------+
| 19658847 | Glanzlichter - CD | NULL | 12.99 | 5 |
| 19658856 | Glanzlichter - CD | NULL | 6.99 | NULL |
| 19658865 | Glanzlichter - CD | NULL | 8.99 | NULL |
| 1965886 | Beach Boys '69 - CASSETTE | NULL | 6.99 | 4.5 |
+----------+---------------------------+-------------+--------------+-----------------------+
4 rows in set (0.00 sec)
