How to store missing FLOAT values with NULL in SQL - mysql

Question

In the other question, I asked about why non-empty values become NULL. But in this question, I asked about how I could make empty values become NULL but not zero.
I found that missing float values are always represented as 0, but not NULL. How could I change that?
The following are the codes with which I created the table and loaded data.
CREATE TABLE Products(sku INTEGER, name VARCHAR(255), description TEXT,
regularPrice FLOAT,
customerReviewAverage FLOAT default NULL );
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);
This is a sample of data in product.csv.
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

Answer 1

The issue is how MySQL interprets an empty field vs a missing field. From the docs for LOAD DATA INFILE...
If an input line has too few fields, the table columns for which input fields are missing are set to their default values.
An empty field value is interpreted different from a missing field. For string types, the column is set to the empty string. For numeric types, the column is set to 0.
In this case it seems MySQL considers it to be empty. You can see this from 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)
Whereas if we remove the trailing commas so the field is missing...
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
Then the data is set to null.
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)
Doing the same thing for #customerReviewAverage as for #description worked for me in 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)