MySQL load NULL values from CSV data

mysql csv load-data-infile

I have a file that can contain from 3 to 4 columns of numerical values which are separated by comma. Empty fields are defined with the exception when they are at the end of the row:

1,2,3,4,5
1,2,3,,5
1,2,3

The following table was created in MySQL:

+-------+--------+------+-----+---------+-------+
| Field | Type   | Null | Key | Default | Extra |
+-------+--------+------+-----+---------+-------+
| one   | int(1) | YES  |     | NULL    |       | 
| two   | int(1) | YES  |     | NULL    |       | 
| three | int(1) | YES  |     | NULL    |       | 
| four  | int(1) | YES  |     | NULL    |       | 
| five  | int(1) | YES  |     | NULL    |       | 
+-------+--------+------+-----+---------+-------+

I am trying to load the data using MySQL LOAD command:

LOAD DATA INFILE '/tmp/testdata.txt' INTO TABLE moo FIELDS 
TERMINATED BY "," LINES TERMINATED BY "\n";

The resulting table:

+------+------+-------+------+------+
| one  | two  | three | four | five |
+------+------+-------+------+------+
|    1 |    2 |     3 |    4 |    5 | 
|    1 |    2 |     3 |    0 |    5 | 
|    1 |    2 |     3 | NULL | NULL | 
+------+------+-------+------+------+

The problem lies with the fact that when a field is empty in the raw data and is not defined, MySQL for some reason does not use the columns default value (which is NULL) and uses zero. NULL is used correctly when the field is missing alltogether.

Unfortunately, I have to be able to distinguish between NULL and 0 at this stage so any help would be appreciated.

Thanks S.

edit

The output of SHOW WARNINGS:

+---------+------+--------------------------------------------------------+
| Level   | Code | Message                                                |
+---------+------+--------------------------------------------------------+
| Warning | 1366 | Incorrect integer value: '' for column 'four' at row 2 | 
| Warning | 1261 | Row 3 doesn't contain data for all columns             | 
| Warning | 1261 | Row 3 doesn't contain data for all columns             | 
+---------+------+--------------------------------------------------------+

With data schema changes like that I would use d6tstack which aligns all columns before running LOAD DATA. See d6tstack SQL examples section on data schema changes.

Jacob

This will do what you want. It reads the fourth field into a local variable, and then sets the actual field value to NULL, if the local variable ends up containing an empty string:

LOAD DATA INFILE '/tmp/testdata.txt'
INTO TABLE moo
FIELDS TERMINATED BY ","
LINES TERMINATED BY "\n"
(one, two, three, @vfour, five)
SET four = NULLIF(@vfour,'')
;

If they're all possibly empty, then you'd read them all into variables and have multiple SET statements, like this:

LOAD DATA INFILE '/tmp/testdata.txt'
INTO TABLE moo
FIELDS TERMINATED BY ","
LINES TERMINATED BY "\n"
(@vone, @vtwo, @vthree, @vfour, @vfive)
SET
one = NULLIF(@vone,''),
two = NULLIF(@vtwo,''),
three = NULLIF(@vthree,''),
four = NULLIF(@vfour,'')
;

I really like this answer. Users can see empty strings '' when they download a csv (using IFNULL(Col,'') in SELECT INTO OUTFILE query) for excel but then uploads accept them as null vs having to deal with \N in the csv. Thanks!

for dates I used 'NULLIF(STR_TO_DATE(@date1, "%d/%m/%Y"), "0000-00-00")'

I have a csv file that contains zeros 0 that should be converted to NULL (because it is not possible to have zero value for the data in question) and also empty strings. How to make sure that both zeros and empty strings are converted to NULL?

How to do this without mentioning specific columns? just for all?

what if you have 50 columns? setting up 50 columns seems overkill. is there a global way of telling Load function to just replace empty values with null?

Janci

MySQL manual says:

When reading data with LOAD DATA INFILE, empty or missing columns are updated with ''. If you want a NULL value in a column, you should use \N in the data file. The literal word “NULL” may also be used under some circumstances.

So you need to replace the blanks with \N like this:

1,2,3,4,5
1,2,3,\N,5
1,2,3

Thanks for the tip - I am sceptical to edit the raw source data but if this is the only way around it I will try it out.

I understand your scepticism, no one likes editing raw data, it just doesn't feel right. However, if you think about it for a minute, there has to be a way to distinguish between NULL and empty string. Should blank entries be translated to NULLs, you'd need a special sequence for empty string. It would nice to have a way how to tell MySQL how to treat blank entries though, something like LOAD DATA INFILE '/tmp/testdata.txt' INTO TABLE moo TREAT BLANKS AS NULL...

OK, but if you have Fields enclosed by: " is that "\N" of "name",\N,"stuff"

I can verify that at least for "phpMyAdmin 3.5.5" no style of \N is accepted as denoting NULL. Instead use NULL, as in this example: "name","age",NULL,"other","stuff"

We have MySQL 5.5.46-0+deb8u1. I tried both NULL and \N, and only \N worked for us.

Dobi

The behaviour is different depending upon the database configuration. In the strict mode this would throw an error else a warning. Following query may be used for identifying the database configuration.

mysql> show variables like 'sql_mode';

Thanks! I was scratching my head trying to work out why importing a CSV with empty columns I'd successfully imported on the production server yesterday wasn't working on my brand-new local installation - this was the answer in my case!

Sam Goldman

Preprocess your input CSV to replace blank entries with \N.

Attempt at a regex: s/,,/,\n,/g and s/,$/,\N/g

Good luck.

This regex partially works, it doesn't solve sequential blank entries, for example ,,,, will be ,\n,,\n, Should be usable if you run it twice

Will summarize the answer and previous comment. Following worked for me, in the order: sed -i 's/,,/,\N/g' $file, sed -i 's/,,/,/g' $file, sed -i 's/\N,$/\N/g' $file,

I would like to do this, but I am not clear on how you are running this regex. If you are using MySQL to run this against the file this would be the best solution. But you don't say and I don't want to spend a bunch of time googling how to do something that may not be possible.

Sunny Sharma

show variables

Show variables like "`secure_file_priv`";

Note: keep your csv file in location given by the above command.

create table assessments (course_code varchar(5),batch_code varchar(7),id_assessment int, assessment_type varchar(10), date int , weight int);

Note: here the 'date' column has some blank values in the csv file.

LOAD DATA INFILE 'C:/ProgramData/MySQL/MySQL Server 8.0/Uploads/assessments.csv' 
INTO TABLE assessments
FIELDS TERMINATED BY ',' 
OPTIONALLY ENCLOSED BY '' 
LINES TERMINATED BY '\n' 
IGNORE 1 ROWS 
(course_code,batch_code,id_assessment,assessment_type,@date,weight)
SET date = IF(@date = '', NULL, @date);

Said

(variable1, @variable2, ..) SET variable2 = nullif(@variable2, '' or ' ') >> you can put any condition

This would probably be better as a comment on stackoverflow.com/a/5968530/10376320

Aimnox

Converted the input file to include \N for the blank column data using the below sed command in UNix terminal:

sed -i 's/,,/,\\N,/g' $file_name

and then use LOAD DATA INFILE command to load to mysql

MySQL load NULL values from CSV data

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