MySQL: How to export data to csv with column headers

I recently had to export a whole number of tables from a MySQL database into .csv files, but to my surprise (or should I say disgust), exporting to .csv with headers is not possible by simply using to the “SELECT … INTO OUTFILE” syntax.  Fortunately all is not lost, although to me this is more proof that MySQL is not really suitable for large applications. Here is how I solved the problem.

I created a table (`tables_to_export`) with a single `tablename` column which I populated with the names of the tables that I wanted to export.  I then created a procedure to traverse this table by means of a cursor so I could build the sql statements required to get the desired export result.

Basically the trick is to create a text string of comma separated column names that is used to create a select union statement to combine the column names with the data.  There are quite a few examples of doing this with a single table and known column names, but I wanted to do this for a whole lot of tables in a loop.  I also need to repeat this export in future, so it made sense to automate the process.

Note: The ‘information_scheme’ database contains a ‘columns’ table that has all the column names, so I used that to get the names to create the string.  The

CREATE DEFINER=`root`@`localhost` PROCEDURE `export_important_tables` _
     (IN `quote` TINYTEXT, IN `delimiter` TINYTEXT, IN `export_dir` VARCHAR(200))
 COMMENT 'Export in csv format with headers'
/* This procedure has been created to add the column names as a header column 
   when exporting mysql tables.
   A table, 'tables_to_export', contains the list of tables to be exported

Usage example: CALL export_important_tables('"',',','/tmp/');

-- Declare some variables
   DECLARE myFile CHAR(30);
   DECLARE curs CURSOR FOR SELECT * FROM `foodmedb`.`tables_to_export`;
-- Declare a cursor
-- There don't need to be set (@variables don't exist outside the procedure, 
-- but I set them for easy reference anyway
   SET @myResult = '';
   SET @myHeader = '';
   SET @myCommand = '';
   SET @myCombined = '';

-- Do some very simple checking for valid parameters
   IF LENGTH(`quote`) > 1 THEN 
       SELECT 'Parameter Error:  may not be more than 1 character';
       LEAVE cont;
   ELSEIF `quote` = '' THEN SET `quote` = '"';
   END IF;

   IF LENGTH(`delimiter`) > 1 THEN 
       SELECT 'Parameter Error:  may not be more than 1 character';
       LEAVE cont;
   ELSEIF `delimiter` = '' THEN SET `delimiter` = ',';
   END IF;

   IF RIGHT(`export_dir`,1) != '/' THEN 
       SELECT 'Paramater Error:  has to end in a /';
       LEAVE cont;
   ELSEIF LENGTH(`export_dir`) = 0 THEN SET `export_dir` = '/tmp';
   END IF;

-- Initialise the cursor query
OPEN curs;

-- Set up a loop so we can traverse all the row in the cursor table
table_loop: LOOP

-- Get a filename
   FETCH curs INTO myFile;
   IF done THEN
      LEAVE table_loop;
   END IF;
-- Build a sql statement string that concatenates the column names from the 
-- information schema's 'columns' table to build a header for the csv file
   SET @myHeader = concat('SELECT GROUP_CONCAT(',char(39),`quote`,char(39),',
   COLUMN_NAME, ', char(39),`quote`,char(39), ' SEPARATOR ', char(39),`delimiter`,
   char(39),') FROM `INFORMATION_SCHEMA`.`COLUMNS` WHERE table_schema=',char(39),
   'foodmedb',char(39),' and table_name=',char(39),myFile,char(39),
   ' INTO @myResult');
   PREPARE stmt1 FROM @myHeader;
   EXECUTE stmt1;
-- Build the the sql statement string that will dump the data into the csv file
   SET @myCommand = concat('SELECT * FROM foodmedb.', myFile, ' into OUTFILE ', 
   char(39), `export_dir`, myFile, '-', DATE_FORMAT(now(),'%Y%m%d-%H%i%s'), '.csv',
   char(39), ' FIELDS TERMINATED BY ', char(39), `delimiter`, char(39), 
   ' OPTIONALLY ENCLOSED BY ', char(39), `quote`, char(39), ' LINES TERMINATED BY ',
-- Use Union to combine the two parts
   SET @myCombined = concat('SELECT ', @myResult,' UNION ALL ',@myCommand);
   PREPARE stmt2 FROM @myCombined;
-- Sweet, now the files are being written!
   EXECUTE stmt2;


CLOSE curs;


This stored procedure should function as it is above.  I have created parameters and some simple error checking to assist with using it more generally than just my particular use.

Please make suggestions and improvements and post them in a comment if you’d like.

About these ads

2 thoughts on “MySQL: How to export data to csv with column headers

    1. Since all the fields are “quoted”, it should not be a problem. However, you can edit this line:

      ELSEIF `delimiter` = ” THEN SET `delimiter` = ‘,’;

      and change the comma to whatever default delimiter you want and then don’t specify any delimiter when you call the procedure.

      Will that work? What delimiter where you looking for?

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s