Mysql

NAME
SYNOPSIS
OBSOLETE SOFTWARE
DESCRIPTION

No close statement
Error messages
The -w switch
->quote($str [, $length])
NULL fields
Metadata
Database Handle
Statement Handle
New in mSQL 2.0
@EXPORT
Displaying whole tables in one go
Version information
Administration
StudlyCaps

PREREQUISITES
COMPATIBILITY NOTES
AUTHORS
SEE ALSO

NAME

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 a separate module. Instead it is emulated using the DBI drivers. You are strongly encouraged to implement new code with DBI directly. See COMPATIBILITY NOTES 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 implemented 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 performance 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 command, or if you want to change the connection to a different database using a database handle you have got from a previous connect, then use selectdb.

  $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 column 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).

No close statement

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 connection). So if you want to free the result or close the connection, 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 corresponding 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 nothing to be added.

By default errors are printed as warnings. You can suppress this behaviour by using the PrintError attribute of the respective handles:

    $dbh->{'dbh'}->{'PrintError'} = 0;

->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. Currently (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 metadata.

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 for mSQL.

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 perlldsc 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];

New in mSQL 2.0

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 namespace. 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 statement 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
control characters: are mapped into their backslashed octal representation
backslashes: are doubled (\\ instead of \)
numeric values: are adjusted right (both integer and floating point values)

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.

The mSQL API implements methods to access some internal configuration parameters: gethostinfo, getserverinfo, and getprotoinfo. All three are available both as class methods 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 commands 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 ListTables 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 David Hughes. To use the adaptor you definitely have to 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

    Msql->getserverinfo

as static methods. This is no longer the case, it never was for MysqlPerl. Instead you have to use

    $dbh->errmsg

    $dbh->getserverinfo

$M(Y)SQL::QUIET

This variable used to turn off the printing of error messages. Unfortunately DBI uses a completely different mechanism for that: The PrintError attribute of the database and/or statement handles. We try to emulate 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;

    $sth->{'PrintError'} = 0;

AUTHORS

Andreas Koenig koenig@franz.ww.TU-Berlin.DE wrote the original MsqlPerl. Jochen Wiedmann wrote the M(y)sqlPerl emulation using DBI.