Msql / Mysql - Perl interfaces to the mSQL and mysql
databases
SYNOPSIS
use Msql;
$dbh = Msql->connect($host);
$dbh = Msql->connect($host, $database);
or
use Mysql;
$dbh = Mysql->connect(undef, $database, $user, $password);
$dbh = Mysql->connect($host, $database, $user, $password);
or
$dbh = Msql1->connect($host);
$dbh = Msql1->connect($host, $database);
$dbh->selectdb($database);
@arr = $dbh->listdbs;
@arr = $dbh->listtables;
$quoted_string = $dbh->quote($unquoted_string);
$error_message = $dbh->errmsg;
$error_number = $dbh->errno; # MySQL only
$sth = $dbh->listfields($table);
$sth = $dbh->query($sql_statement);
@arr = $sth->fetchrow; # Array context
$firstcol = $sth->fetchrow; # Scalar context
@arr = $sth->fetchcol($col_number);
%hash = $sth->fetchhash;
$sth->dataseek($row_number);
$sth->as_string;
@indices = $sth->listindices # only in mSQL 2.0
@arr = $dbh->listindex($table,$index) # only in mSQL 2.0
($step,$value) = $dbh->getsequenceinfo($table) # only in mSQL 2.0
$rc = $dbh->shutdown();
$rc = $dbh->createdb($database);
$rc = $dbh->dropdb($database);
OBSOLETE SOFTWARE
As of Msql-Mysql-modules 1.19_10 M(y)sqlPerl is no longer
drivers. You are strongly encouraged to implement new code
with DBI directly. See the COMPATIBILITY NOTES entry else
where in this document below.
DESCRIPTION
This package is designed as close as possible to its C API
counterpart. The manual that comes with mSQL or MySQL
describes most things you need. Due to popular demand it
was decided though, that this interface does not use
StudlyCaps (see below).
As of March 1998, the Msql and Mysql modules are obsoleted
by the DBI drivers DBD::mSQL and DBD::mysql, respectively.
You are strongly encouraged to implement new code with the
DBI drivers. In fact, Msql and Mysql are currently imple
mented as emulations on top of the DBI drivers.
Internally you are dealing with the two classes `Msql' and
`Msql::Statement' or `Mysql' and `Mysql::Statement',
respectively. You will never see the latter, because you
reach it through a statement handle returned by a query or
a listfields statement. The only class you name explicitly
is Msql or Mysql. They offer you the connect command:
$dbh = Msql->connect($host);
$dbh = Msql->connect($host, $database);
or
$dbh = Mysql->connect($host, undef, $user, $password);
$dbh = Mysql->connect($host, $database, $user, $password);
or
$dbh = Msql1->connect($host);
$dbh = Msql1->connect($host, $database);
This connects you with the desired host/database. With no
argument or with an empty string as the first argument it
connects to the UNIX socket, which has a much better per
formance than the TCP counterpart. A database name as the
second argument selects the chosen database within the
connection. The return value is a database handle if the
connect succeeds, otherwise the return value is undef.
You will need this handle to gain further access to the
database.
$dbh->selectdb($database);
If you have not chosen a database with the `connect' com
mand, or if you want to change the connection to a differ
ent database using a database handle you have got from a
$sth = $dbh->listfields($table);
$sth = $dbh->query($sql_statement);
These two work rather similar as descibed in the mSQL or
MySQL manual. They return a statement handle which lets
you further explore what the server has to tell you. On
error the return value is undef. The object returned by
listfields will not know about the size of the table, so a
numrows() on it will return the string "N/A";
@arr = $dbh->listdbs();
@arr = $dbh->listtables;
An array is returned that contains the requested names
without any further information.
@arr = $sth->fetchrow;
returns an array of the values of the next row fetched
from the server. Be carefull with context here! In scalar
context the method behaves different than expected and
returns the first column:
$firstcol = $sth->fetchrow; # Scalar context!
Similar does
%hash = $sth->fetchhash;
return a complete hash. The keys in this hash are the col
umn names of the table, the values are the table values.
Be aware, that when you have a table with two identical
column names, you will not be able to use this method
without trashing one column. In such a case, you should
use the fetchrow method.
@arr = $sth->fetchcol($colnum);
returns an array of the values of each row for column
$colnum. Note that this reads the entire table and leaves
the row offset at the end of the table; be sure to use
$sth->dataseek() to reset it if you want to re-examine the
table.
$sth->dataseek($row_number);
lets you specify a certain offset of the data associated
with the statement handle. The next fetchrow will then
return the appropriate row (first row being 0).
Whenever the scalar that holds a database or statement
handle loses its value, Msql chooses the appropriate
action (frees the result or closes the database connec
tion). So if you want to free the result or close the con
nection, choose to do one of the following:
undef the handle
use the handle for another purpose
let the handle run out of scope
exit the program.
Error messages
Both drivers, Msql and Mysql implement a method
->errmsg(), which returns a textual error message. Mysql
additionally supports a method ->errno returning the cor
responding error number.
Usually you do fetch error messages with
$errmsg = $dbh->errmsg();
In situations where a $dbh is not available (for example
when connect() failed) you may instead do a
$errmsg = Msql->errmsg();
or
$errmsg = Mysql->errmsg();
or
$errmsg = Msql1->errmsg();
The `-w' switch
With Msql and Mysql the `-w' switch is your friend! If you
call your perl program with the `-w' switch you get the
warnings from ->errmsg on STDERR. This is a handy method
to get the error messages from the msql server without
coding it into your program.
If you want to know in greater detail what's going on, set
the environment variables that are described in David's
manual. David's debugging aid is excellent, there's noth
ing to be added.
By default errors are printed as warnings. You can sup
press this behaviour by using the PrintError attribute of
the respective handles:
->quote($str [, $length])
returns the argument enclosed in single ticks ('') with
any special character escaped according to the needs of
the API.
For mSQL this means, any single tick within the string is
escaped with a backslash and backslashes are doubled. Cur
rently (as of msql-1.0.16) the API does not allow to
insert NUL's (ASCII 0) into tables. The quote method does
not fix this deficiency.
MySQL allows NUL's or any other kind of binary data in
strings. Thus the quote method will additionally escape
NUL's as \0.
If you pass undefined values to the quote method, it
returns the string `NULL'.
If a second parameter is passed to `quote', the result is
truncated to that many characters.
NULL fields
NULL fields in tables are returned to perl as undefined
values.
Metadata
Now lets reconsider the above methods with regard to meta
data.
Database Handle
As said above you get a database handle with the connect()
method. The database handle knows about the socket, the
host, and the database it is connected to.
You get at the three values with the methods
$scalar = $dbh->sock;
$scalar = $dbh->host;
$scalar = $dbh->database;
Mysql additionally supports
$scalar = $dbh->user;
$scalar = $dbh->sockfd;
where the latter is the file descriptor of the socket used
by the database connection. This is the same as $dbh->sock
Statement Handle
Two constructor methods return a statement handle:
$sth = $dbh->listfields($table);
$sth = $dbh->query($sql_statement);
$sth knows about all metadata that are provided by the
API:
$scalar = $sth->numrows;
$scalar = $sth->numfields;
@arr = $sth->table; the names of the tables of each column
@arr = $sth->name; the names of the columns
@arr = $sth->type; the type of each column, defined in msql.h
and accessible via Msql::CHAR_TYPE,
&Msql::INT_TYPE, &Msql::REAL_TYPE or
&Mysql::FIELD_TYPE_STRING,
&Mysql::FIELD_TYPE_LONG, ...
@arr = $sth->isnotnull; array of boolean
@arr = $sth->isprikey; array of boolean
@arr = $sth->isnum; array of boolean
@arr = $sth->length; array of the possibble maximum length of each
field in bytes
@arr = $sth->maxlength; array of the actual maximum length of each field
in bytes. Be careful when using this attribute
under MsqlPerl: The server doesn't offer this
attribute, thus it is calculated by fetching
all rows. This might take a long time and you
might need to call $sth->dataseek.
Mysql additionally supports
$scalar = $sth->affectedrows number of rows in database affected by query
$scalar = $sth->insertid the unique id given to a auto_increment field.
$string = $sth->info() more info from some queries (ALTER TABLE...)
$arrref = $sth->isblob; array of boolean
The array methods (table, name, type, is_not_null,
is_pri_key, length, affected_rows, is_num and blob) return
an array in array context and an array reference (see the
perlref manpage and the perlldsc manpage for details) when
called in a scalar context. The scalar context is useful,
if you need only the name of one column, e.g.
$name_of_third_column = $sth->name->[2]
which is equivalent to
@all_column_names = $sth->name;
$name_of_third_column = $all_column_names[2];
The query() function in the API returns the number of rows
affected by a query. To cite the mSQL API manual, this
means...
If the return code is greater than 0, not only does it imply
success, it also indicates the number of rows "touched" by the query
(i.e. the number of rows returned by a SELECT, the number of rows
modified by an update, or the number of rows removed by a delete).
As we are returning a statement handle on selects, we can
easily check the number of rows returned. For non-selects
we behave just the same as mSQL-2.
To find all indices associated with a table you can call
the `listindices()' method on a statement handle. To find
out the columns included in an index, you can call the
`listindex($table,$index)' method on a database handle.
There are a few new column types in mSQL 2. You can access
their numeric value with these functions defined in the
Msql package: IDENT_TYPE, NULL_TYPE, TEXT_TYPE, DATE_TYPE,
UINT_TYPE, MONEY_TYPE, TIME_TYPE, IDX_TYPE, SYSVAR_TYPE.
You cannot talk to a 1.0 server with a 2.0 client.
You cannot link to a 1.0 library and to a 2.0 library at
the same time. So you may want to build two different Msql
modules at a time, one for 1.0, another for 2.0, and load
whichever you need. Check out what the `-I' switch in perl
is for.
Everything else seems to remain backwards compatible.
@EXPORT
For historical reasons the constants CHAR_TYPE, INT_TYPE,
and REAL_TYPE are in @EXPORT instead of @EXPORT_OK. This
means, that you always have them imported into your names
pace. I consider it a bug, but not such a serious one,
that I intend to break old programs by moving them into
EXPORT_OK.
Displaying whole tables in one go
A handy method to show the complete contents of a state
ment handle is the as_string method. This works similar to
the msql monitor with a few exceptions:
the width of a column
is calculated by examining the width of all entries in
that column
are mapped into their backslashed octal representation
backslashes
are doubled (`\\ instead of \')
numeric values
are adjusted right (both integer and floating point val
ues)
The differences are illustrated by the following table:
Input to msql (a real carriage return here replaced with
^M):
CREATE TABLE demo (
first_field CHAR(10),
second_field INT
) \g
INSERT INTO demo VALUES ('new
line',2)\g
INSERT INTO demo VALUES ('back\\slash',1)\g
INSERT INTO demo VALUES ('cr^Mcrnl
nl',3)\g
Output of msql:
+-------------+--------------+
| first_field | second_field |
+-------------+--------------+
| new
line | 2 |
| back\slash | 1 |
crnlr
nl | 3 |
+-------------+--------------+
Output of pmsql:
+----------------+------------+
|first_field |second_field|
+----------------+------------+
|new\012line | 2|
|back\\slash | 1|
|cr\015crnl\012nl| 3|
+----------------+------------+
Version information
The version of Msql and Mysql is always stored in
$Msql::VERSION or $Mysql::VERSION as it is perl standard.
configuration parameters: gethostinfo, getserverinfo, and
getprotoinfo. All three are available both as class meth
ods or via a database handle. But under no circumstances
they are associated with a database handle. All three
return global variables that reflect the last connect()
command within the current program. This means, that all
three return empty strings or zero before the first call
to connect().
This situation is better with MySQL: The methods are valid
only in connection with a database handle.
Administration
shutdown, createdb, dropdb, reloadacls are all accessible
via a database handle and implement the corresponding
methods to what msqladmin does.
The mSQL and MySQL engines do not permit that these com
mands are invoked by users without sufficient privileges.
So please make sure to check the return and error code
when you issue one of them.
$rc = $dbh->shutdown();
$rc = $dbh->createdb($database);
$rc = $dbh->dropdb($database);
It should be noted that database deletion is not prompted
for in any way. Nor is it undo-able from within Perl.
B<Once you issue the dropdb() method, the database will be gone!>
These methods should be used at your own risk.
StudlyCaps
Real Perl Programmers (C) usually don't like to type List
Tables but prefer list_tables or listtables. The mSQL API
uses StudlyCaps everywhere and so did early versions of
MsqlPerl. Beginning with $VERSION 1.06 all methods are
internally in lowercase, but may be written however you
please. Case is ignored and you may use the underline to
improve readability.
The price for using different method names is neglectible.
Any method name you use that can be transformed into a
known one, will only be defined once within a program and
will remain an alias until the program terminates. So feel
free to run fetch_row or connecT or ListDBs as in your old
programs. These, of course, will continue to work.
PREREQUISITES
mSQL is a database server and an API library written by
install these first.
MySQL is a libmysqlclient.a library written by Michael
Widenius This was originally inspired by MySQL.
COMPATIBILITY NOTES
M(y)sql used to be a separate module written in C. This is
no longer the case, instead the old modules are emulated
by their corresponding DBI drivers. I did my best to
remove any incompatibilities, but the following problems
are known to remain:
Static methods
For whatever reason, mSQL implements some functions
independent from the respective database connection
that really depend on it. This made it possible to
implement
Msql->errmsg
or
Msql->getserverinfo
as static methods. This is no longer the case, it
never was for MysqlPerl. Instead you have to use
$dbh->errmsg
or
$dbh->getserverinfo
$M(Y)SQL::QUIET
This variable used to turn off the printing of error
messages. Unfortunately DBI uses a completely differ
ent mechanism for that: The `PrintError' attribute of
the database and/or statement handles. We try to emu
late the old behaviour by setting the `PrintError'
attribute to the current value of $M(Y)SQL::QUIET when
a handle is created, that is when M(y)sql->connect or
$dbh->query() are called.
You can overwrite this by using something like
$dbh->{'dbh'}->{'PrintError'} = 1;
or
$sth->{'PrintError'} = 0;
Andreas Koenig `koenig@franz.ww.TU-Berlin.DE' wrote the
original MsqlPerl. Jochen Wiedmann `joe@ispsoft.de' wrote
the M(y)sqlPerl emulation using DBI.
SEE ALSO
Alligator Descartes wrote a database driver for Tim
Bunce's DBI. I recommend anybody to carefully watch the
development of this module (`DBD::mSQL'). Msql is a sim
ple, stable, and fast module, and it will be supported for
a long time. But it's a dead end. I expect in the medium
term, that the DBI efforts result in a richer module fam
ily with better support and more functionality. Alligator
maintains an interesting page on the DBI development:
http://www.symbolstone.org/technology/perl/DBI
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