How to load null data with file? - mysql

Question

Create sample database and table to use with.
create database `test`;
use `test`;
create table `test` (`value` float(10,2) null);
insert into test (value) values (null);
select value from test;
+-------+
| value |
+-------+
| NULL |
+-------+
1 row in set (0.00 sec)
Now i want to create a txt file ,when you load it ,null data can be loaded into the test table.
delete from test;
Here is my data file named test.txt showed in vim(:set list).
Load the file into table.
LOAD DATA LOCAL INFILE "test.txt"
INTO TABLE test
FIELDS TERMINATED BY '\t'
LINES TERMINATED BY '\n' \w;
select value from test;
+-------+
| value |
+-------+
| 0.00 |
| 0.00 |
| 0.00 |
| 0.00 |
| 0.00 |
+-------+
How to load null data for value field with file in my case?
How to create this kind of data file,the value field is null after you load it?
The runtime environment:win10+mysql-5.7.
select version();
+-----------+
| version() |
+-----------+
| 5.7.22 |
+-----------+
1 row in set (0.03 sec)
Show test.txt file in vim with set list.
\N$
\N^I$
case:without set
Load it without (value) SET value = (CASE WHEN #value IS NULL THEN NULL ELSE #value END).
LOAD DATA LOCAL INFILE "f:/test.txt"
INTO TABLE test
FIELDS TERMINATED BY '\t'
LINES TERMINATED BY '\n' \W;
OUTPUT:
Warning (Code 1265): Data truncated for column 'value' at row 1
Warning (Code 1262): Row 2 was truncated; it contained more data than there were input columns
select * from test;
+-------+
| value |
+-------+
| 0.00 |
| NULL |
+-------+
case:with set
Load it with (value) SET value = (CASE WHEN #value IS NULL THEN NULL ELSE #value END).
delete from test;
LOAD DATA LOCAL INFILE "f:/test.txt"
INTO TABLE test
FIELDS TERMINATED BY '\t'
LINES TERMINATED BY '\n'
(value)SET value = (CASE WHEN #value IS NULL THEN NULL ELSE #value END) \W;
OUTPUT:
Warning (Code 1265): Data truncated for column 'value' at row 1
Warning (Code 1262): Row 2 was truncated; it contained more data than there were input columns
select * from test;
+-------+
| value |
+-------+
| NULL |
| NULL |
+-------+
Thank #Schwern.
LOAD DATA LOCAL INFILE "f:/test.txt"
INTO TABLE test
FIELDS TERMINATED BY '\t'
LINES TERMINATED BY '\r\n' \W;
Either works fine with no warnings.

Answer 1

You can use \N.
The problem is all your input lines have an extra empty field. Tab terminates the field, like a comma. You've used it as if it encloses it like quotes. For example, your first line ^Inull^I is three fields. The first is empty. The second contains null. And the third is empty.
MySQL should have said something like
Query OK, 5 rows affected, 8 warnings (0.01 sec)
Records: 5 Deleted: 0 Skipped: 0 Warnings: 8
You can read those warnings with show warnings.
+---------+------+---------------------------------------------------------------------------+
| Level | Code | Message |
+---------+------+---------------------------------------------------------------------------+
| Warning | 1265 | Data truncated for column 'value' at row 1 |
| Warning | 1262 | Row 1 was truncated; it contained more data than there were input columns |
| Warning | 1265 | Data truncated for column 'value' at row 2 |
| Warning | 1262 | Row 2 was truncated; it contained more data than there were input columns |
| Warning | 1265 | Data truncated for column 'value' at row 3 |
| Warning | 1265 | Data truncated for column 'value' at row 4 |
| Warning | 1262 | Row 4 was truncated; it contained more data than there were input columns |
| Warning | 1265 | Data truncated for column 'value' at row 5 |
+---------+------+---------------------------------------------------------------------------+
All you need is this:
\N$
Note that lines terminated by is sensitive to Unix vs Windows newlines. From the docs...
If you have generated the text file on a Windows system, you might have to use LINES TERMINATED BY '\r\n' to read the file properly, because Windows programs typically use two characters as a line terminator.
This explains the warnings you are getting.