Aug
Extract a Single Table from a mysqldump File
Posted by Jared in Tips & TricksTagged: geek talk, mysql, the geeks
A little while back, I wrote this article that explained some awk magic for extracting the restore information for a single table from a mysqldump file. Since then I’ve created a Perl script that accomplishes the same thing, but is a little more flexible. The Perl script is available for download here. I’ve tested it on Linux, but it should work from Windows as well if you have Perl installed. So now you have three options when needing to get one table out of your mysqldump file.
Method 1: Perl script
This script will parse a full mysqldump file and extract the necessary portions required to restore a single table. The output is printed to STDOUT, so you’ll want to redirect to a file from the command line, like so: extract_sql.pl > somefile.sql
Usage Summary (run the script with no parameters and you’ll see this):
Usage: extract_sql.pl -t <table name> -r <restore file> [options] Required: -t <table name> table name to extract from the file Optional: -r <restore file> mysqldump file that you want to parse. Uses STDIN if nothing is specified --listTables If set, then a list of tables existing in your restore file is returned, and no other actions are taken --noExtras If set, then extra cmds at top of mysqldump file will not be included (such as disabling foreign key checks). Usually you will want these things changed before restoring a table, so the default is for these to be included. -v verbosity - use multiple times for greater effect -h Display this help message
So, to extract the info needed to restore table ‘mytable’ from the mysqldump file ‘mydumpfile’, you’d run:
extract_sql.pl -t mytable -r mydumpfile > mytable.sql
or, if your dump file is gzipped, you could save a little time and space by doing:
cat mydumpfile.gz | gunzip | extract_sql.pl -t mytable > mytable.sql
To see what table names are within your mysqldump file, run:
extract_sql.pl –listTables -r mydumpfile
The script has a lot of extra functions, etc. in it for logging and cmd-line parsing, but the meat of what it does is here (NOTE! This is not the entire script, just an excerpt of it, use the download link near the beginning of this file to obtain the entire script to use it yourself):
if ($conf{'restoreFile'}) {
## open the mysqldump file
open(STDIN, "< $conf{'restoreFile'}") || quit("ERROR => Couldn't open file $conf{'restoreFile'}: $!", 3);
}
my $flag = 0;
## go through the file one line at a time
while (my $line = <stdin>) {
if ($conf{'listTables'}) {
if ($line =~ /^-- Table structure for table `(.*)`/) {
print $1 . "\n";
}
}
else {
## if we're not ignoring extra lines, and we haven't set the flag, and if it's not a 40000 code, then print
if (!$conf{'noExtras'} &amp;&amp; !$flag) {
if ($line =~ /^\/\*!(.....).*\*\//) { print $line unless ($1 == 40000); }
}
## set a flag when we encounter the table we want
if ($line =~ /^-- Table structure for table `$conf{'tableName'}`/) {
$flag = 1;
printmsg("Turning flag on", 1);
}
## turn flag off as soon as we encounter next table definition
elsif ($line =~ /^-- Table structure for table/) {
$flag = 0;
printmsg("Turning flag off", 1);
}
## if flag is set, then print to STDOUT, otherwise just move on
if ($flag) {
print $line;
}
}
}
Method 2: awk
First, you have to know where in your mysqldump output you want to begin your extraction, and where you want to end it. The key here is finding something unique at the beginning and ending of the block that won’t be found anywhere else.
A sample mysqldump contains something like the following:
-- -- Table structure for table `test1` -- ... DROP TABLE IF EXISTS `test1`; CREATE TABLE `test1` ( ... LOCK TABLES `test1` WRITE; INSERT INTO `test1` VALUES (1,0,’2 ... UNLOCK TABLES; ... –- –- Table structure for table `test2` –-
As you can see, we have a line with the comment “Table structure for table `test1`”, then all of the dropping, creating, and inserting for the table, and then another comment for the next table. These two lines are perfect for grabbing all of the operations pertinent to our one table.
To extract the dump for a single table from an entire database dump, run the following from a command prompt:
$ awk ‘/Table structure for table .test1./,/Table structure for table .test2./{print}’ mydumpfile.sql > /tmp/extracted_table.sql
The above command searches through the dump file, and as soon as it matches a line containing the first search string (denoted by the first set of slashes), it prints that line and every subsequent line until it encounters a line containing the second search string (denoted by the second set of slashes). FYI, the periods surrounding the table names above are wildcard characters.
Now the extracted_table.sql file contains the SQL to restore your table. One final thing: There are usually various parameters at the top of your mysqldump file that you may need to set before restoring your table, depending on the complexity of your database (i.e. disabling foreign key checks.)
To restore your table, you’d run:
$ mysql -u user -ppassword mydb < /tmp/extracted_table.sql
Voila! – you’re back in business.
Method 3: Restore elsewhere and extract
Another option is to restore your data into a temporary database (assuming you have the disk space), extract the table you’re interested in to it’s own dump file, and then restore that dump file to your original database.
Create a new database, name it something easy to distinguish from your production one, i.e. fakedb.
Restore your data to the fakedb with a command like this:
$ mysql -u user -ppassword fakedb < mydumpfile.sql
From fakedb, grab the data you want from your target table:
mysql> select * from targettable into outfile “/tmp/mytablebackup.bak”;
On the production db, where you have your undesired data, clear it all out with:
mysql> delete from baddatatable;
Import the good stuff back into it:
mysql> load data infile “/tmp/mytablebackup.bak” into table baddatatable;
Now you can rinse and repeat if you want to keep trying whatever your initial operation was until you perfect it. Make your changes, delete everything, load it back in, redeux.
Hope this is useful.
