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What does a max_data_length of "null" mean when you do a show table? Do MY SQL tables auto grow or do you need to keep allocating additional space?

@ Thomas :
NULL = unlimited;
In some case ( max configs for row, col, memory, disk space, buffer ... ), 0 or Null in MySQL config mean no limit, or max limit ( so the real limit is the software, or bad way, the hardware limit ).
Unlimited setting is not recommanded, on httpd server that u cant control in real time.
Use unlimited, when you can restart, stop, mysql or the server ( i use that setting only on local server )

If you need to get hold of only one of these columns, there are sometimes another way. E.g. if you don't need row format, type, name, average row length and all the other stuff, but only want to see the total number of rows in a table, use COUNT(*).

I was looking for a way to show the relationship of tables based on unique key, key, index, and foreign key constraints. I found that I can get some of the data using the admin statement SHOW INDEX FROM <<TBL>>. However this will give only the index name and the Column_name in the table that I am requesting from. I then did a SHOW CREATE TABLE <<TBL>> and this dumps the DDL script used to create the table. I would have to parse this information but could get everything I needed. I then found that SHOW TABLE STATUS LIKE <<TBL>> gave me The REFER information mapped to the column name. Unfortunatlly it did so in the Comments field as a string so uh! more parsing. This is what I have been able to discover so far and am still looking for a clean way to gather key, index, and constraint information to dynamically build table relationships. Also I noticed that the constraint names set in the DDL have not been preserved and mysql has given the constraints their own names. Names given keys are preserved. you can see this by running the show create table <<TBL>> on any table you have set constraints on.

Example for only one table:
SHOW TABLE STATUS from name_db like 'table_name';
=similarly=
SHOW TABLE STATUS from name_db like '_able-na%';
quotation marks in LIKE is obligatory

Here is an example of using this command with php and get results...

<?php

mysql_connect("localhost","root","");
$result = mysql_query("SHOW TABLE STATUS FROM test;");
while($array = mysql_fetch_array($result)) {
$total = $array[Data_length]+$array[Index_length];
echo '
Table: '.$array[Name].'<br />
Data Size: '.$array[Data_length].'<br />
Index Size: '.$array[Index_length].'<br />
Total Size: '.$total.'<br />
Total Rows: '.$array[Rows].'<br />
Average Size Per Row: '.$array[Avg_row_length].'<br /><br />
';
}

?>

Here is a perl script to add up free space per engine. Whether you are out of space depends on how you have configured MySQL. The InnoDB engine might be limited space, or it might be allowed to grow. The MyISAM space is probably in the file system, which has as much left as it has.

This script is a hack. Feel free to improve and post.

For some reason, I can't get it to format nicely, either.

#!/opt/gnu/bin/perl -w

use strict;

use Getopt::Long;
my @options;

# Get output immediately. It won't hurt performance.
use FileHandle;
autoflush STDERR;
autoflush STDOUT;

my $pw;
push(@options, "password=s", \$pw);

my $host = "localhost";
push(@options, "host=s", \$host);

die "Couldn't parse options" if !GetOptions(@options);

die "Must give -password\n" if !defined($pw);

my $cmd = mysql_cmd("show databases");
open(CMD, $cmd) or die "Couldn't $cmd: $!\n";
my @databases;
my $header = <CMD>;
while ( <CMD> ) {
s/[\r\n]$//g;
#print "$_\n";
push (@databases, $_);
}
close(CMD);

#print "@databases";

my %colmap = ( 'Data_length' => 6,
'Index_length' => 8,
'Engine' => 1,
'Comment' => 17 );

my %size;
my %total_size;
my %engine_map;

my $inno_db_free;
foreach my $db (@databases) {
print STDERR ".";
$cmd = mysql_cmd("use $db; show table status");

open(CMD, $cmd) or die "Couldn't $cmd: $!\n";
my $header = <CMD>;
my $total_size = 0;
if (defined($header)) {
$header =~ s/[\r\n]$//g;
my @head = split("\t", $header);

foreach my $col (keys %colmap) {
die "$db: Expected '$col', found '" . $head[$colmap{$col}] . "'"
if $head[$colmap{$col}] ne $col;
}

while (<CMD>) {
my @data = split("\t");
my ($data_length, $index_length) = @data[6,8];
my ($engine, $comment) = @data[1,17];
$engine_map{$engine}++;
$size{$db}{$engine} += $data_length + $index_length;
$total_size{$db} += $data_length + $index_length;

if ( $comment =~ /InnoDB free: (\d+) kB/ ) {
die "Found two different inno DB free sized.\n"
if defined($inno_db_free) && $inno_db_free != $1;
$inno_db_free = $1;
}
}
close(CMD);
}
}
print STDERR "\n";

print "NOTE: All numbers are in megabytes (M).\n";
printf("Inno DB free: %.1f\n", $inno_db_free / 1024)
if defined($inno_db_free);

printf("%-30s ", "database");
foreach my $engine (sort keys(%engine_map)) {
printf "%7s ", $engine;
}
printf "%8s", "total";
print "\n";

foreach my $db (sort {$total_size{$b} <=> $total_size{$a}} keys %total_size) {
printf("%-30s ", $db);
foreach my $engine (sort keys(%engine_map)) {
my $size= $size{$db}{$engine};
$size = 0 if !defined($size);
printf("%7.1f ", $size / 1024 / 1024);
}
printf("%8.1f\n", $total_size{$db} / 1024 / 1024);
}


sub mysql_cmd {
my $mysql_cmd = shift;

return "mysql -uroot -h$host -p$pw -e '$mysql_cmd'|";
}





Example output:

% ./db-space.pl -p ...
....................
NOTE: All numbers are in megabytes (M).
Inno DB free: 10755.0
database HEAP InnoDB MyISAM total
tldan 0.0 339.1 720.3 1059.4
ml3test7 0.0 1010.8 0.0 1010.8
ml3test6 0.0 930.4 0.0 930.4
test 0.0 655.4 0.0 655.4
blarg4 0.0 39.5 0.0 39.5

For InnoDB tables, the Comment field of SHOW TABLE STATUS is useful for extracting foreign key information for older versions of MySQL. For versions since 5.0.6, you can query INFORMATION_SCHEMA. (See http://dev.mysql.com/doc/refman/5.0/en/key-column-usage-table.html)

The way the foreign key info is stored in the Comment field can be a pain to parse. Here's a snippet of PHP code that shows how to do this.

<?php
//DB connection already established
$res = mysql_query("SHOW TABLE STATUS LIKE 'MY_TABLE'");
$row = mysql_fetch_assoc($res);
mysql_free_result($res);
$commentArr = preg_split('/; */', $row['Comment']);

$foreignKeyArr = array(); //<-- We want to fill this.

foreach($commentArr as $comment) {
   //Only work on InnoDB foreign key info.
   if(preg_match(
         '/\(`(.*)`\) REFER `(.*)\/(.*)`\(`(.*)`\)/',
         $comment,
         $matchArr)) {
   $primaryKeyFieldArr = preg_split('/` `/', matchArr[1]);
   $foreignKeyDatabase = $matchArr[2];
   $foreignKeyTable = $matchArr[3];
   $foreignKeyFieldArr = preg_split('/` `/', $matchArr[4]);

   for($i = 0; $i < count($primaryKeyFieldArr); $i++) {
      $foreignKeyArr[ $primaryKeyFieldArr[$i] ] = array(
         'db' => $foreignKeyDatabase,
         'table' => $foreignKeyTable,
         'field' => $foreignKeyFieldArr[$i]);
   }
}
?>

Now $foreignKeyArr holds a list of fields from MY_TABLE
that have a foreign key constraint. If MY_FK is a foreign
key referencing YOUR_ID in YOUR_TABLE, you will get:

$foreignKeyArr['MY_FK']['db'] == 'THIS_DATABASE'
$foreignKeyArr['MY_FK']['table'] == 'YOUR_TABLE'
$foreignKeyArr['MY_FK']['field'] == 'YOUR_ID'

try:

mysql -u <user> --password=<pass> <db_name> -e 'show table status;' | awk '{sum=sum+$7+$9;} END {print sum/1024/1024}'

where <user>, <pass> and <db_name> is your account and database.

returns the size of (sum of) columns Data_length + Index_length in MB

/F

If you are REALLY desperate to get FK relationships you can always use a bit of JAVA code.
I know you Perl guys will balk at this - but the JDBC METADATA can give you this information quite easily.
maybe there is something similar for Perl DBI?
Yes!
http://search.cpan.org/src/TIMB/DBI_AdvancedTalk_2004/sld086.htm

Or you can read the foreign key relationships out of the information_schema. Java's not magic, you know, all that info is in there to be used by anything that can read it. ;-)

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