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MySQL INTO OUTFILE override existing file?

Posted by: admin November 1, 2017 Leave a comment

Questions:

I’ve written a big sql script that creates a CSV file. I want to call a cronjob every night to create a fresh CSV file and have it available on the website.

Say for example I’m store my file in ‘/home/sites/example.com/www/files/backup.csv’

and my SQL is

SELECT * INTO OUTFILE '/home/sites/example.com/www/files/backup.csv'
  FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"'
  LINES TERMINATED BY '\n'
  FROM ( ....

MySQL gives me an error when the file already exists

File ‘/home/sites/example.com/www/files/backup.csv’ already exists

Is there a way to make MySQL overwrite the file?

I could have PHP detect if the file exists and delete it before creating it again but it would be more succinct if I can do it directly in MySQL.

Answers:

No, there’s no way to overwrite it. From the docs:

file_name cannot be an existing file, which among other things prevents files such as /etc/passwd and database tables from being destroyed.

It might be a better idea to use a different filename each night, as having multiple backups means you can recover from problems that have existed for more than a day. You could then maintain a symlink that always points at the latest complete csv.

Questions:
Answers:

Why not rm -f /home/sites/example.com/www/files/backup.csv in the script ran by cron?

You can run this from inside mysql. Just escape to the shell with \!
For example:

Mysql> \! rm -f /home/sites/example.com/www/files/backup.csv

Questions:
Answers:

For a job like this I would place it into a bash file, delete the file

#!/bin/bash
rm /path/to/backup.csv
./backup_sql_query.sh  <<-- This contains the script to backup to CSV.

The better option is to actually add a timestamp though. Disk space isn’t expensive in this day and age.

Questions:
Answers:

There is no way.

Only one possible you can procedure with dynamic statement.

CREATE PROCEDURE export_dynamic(IN file_name char(64)) 
BEGIN 
set @myvar = concat('SELECT * INTO OUTFILE ',"'",file_name,"'",' FROM Table1') ; 
PREPARE stmt1 FROM @myvar; 
EXECUTE stmt1; 
Deallocate prepare stmt1; 
END; 

Questions:
Answers:

Kind of a dated question, but hopefully this will help someone.

Simply escape to a shell from within mysql and execute a rm command to remove the file before you attempt to write it. For example:

Mysql> \! rm -f /home/sites/example.com/www/files/backup.csv

Enjoy!

Questions:
Answers:

3 steps to do this right.
Your backup will be executed every night while you sleep (or not)

STEP 1 : Create a stored procedure for your SQL

CREATE PROCEDURE backupCSV()
SELECT * INTO OUTFILE '/home/sites/example.com/www/files/backup.csv'
FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"'
LINES TERMINATED BY '\n'
FROM ( ....

STEP 2 : Create a script “/home/backupCSV.sh” to delete old file and call the stored procedure

echo "$(date +"%Y-%m-%d %T") START MAINTENANCE SCRIPT "
rm /home/sites/example.com/www/files/backup.csv
echo "$(date +"%Y-%m-%d %T")    SUCCESS >> Old file deleted"
mysql --user=[user] --password=[password] [dataBaseName] --execute="CALL backupCSV();"
echo "$(date +"%Y-%m-%d %T")    SUCCESS >> New file created"
echo "$(date +"%Y-%m-%d %T") END MAINTENANCE SCRIPT "

STEP 3 : Update Crontab to execute the script everyday

# m h dom mon dow user  command

 0   3  * * *   root    sh -x /home/backupCSV.sh

STEP 4 (optionnal) : thanks me 😉