DBD::Sybase.3perl

Langue: en

Version: 2003-04-03 (debian - 07/07/09)

Section: 3 (Bibliothèques de fonctions)

Sommaire

NAME

DBD::Sybase - Sybase database driver for the DBI module

SYNOPSIS

     use DBI;
 
     $dbh = DBI->connect("dbi:Sybase:", $user, $passwd);
 
     # See the DBI module documentation for full details

DESCRIPTION

DBD::Sybase is a Perl module which works with the DBI module to provide access to Sybase databases.

Connecting to Sybase


The interfaces file

The DBD::Sybase module is built on top of the Sybase Open Client Client Library API. This library makes use of the Sybase interfaces file (sql.ini on Win32 machines) to make a link between a logical server name (e.g. SYBASE) and the physical machine / port number that the server is running on. The OpenClient library uses the environment variable SYBASE to find the location of the interfaces file, as well as other files that it needs (such as locale files). The SYBASE environment is the path to the Sybase installation (eg '/usr/local/sybase'). If you need to set it in your scripts, then you must set it in a "BEGIN{}" block:

    BEGIN {
        $ENV{SYBASE} = '/opt/sybase/11.0.2';
    }
 
    $dbh = DBI->connect('dbi:Sybase:', $user, $passwd);

Specifying the server name

The server that DBD::Sybase connects to defaults to SYBASE, but can be specified in two ways.

You can set the DSQUERY environement variable:

     $ENV{DSQUERY} = "ENGINEERING";
     $dbh = DBI->connect('dbi:Sybase:', $user, $passwd);

Or you can pass the server name in the first argument to connect():

     $dbh = DBI->connect("dbi:Sybase:server=ENGINEERING", $user, $passwd);

Specifying other connection specific parameters

It is sometimes necessary (or beneficial) to specify other connection properties. Currently the following are supported:

server
Specify the server that we should connect to 
      $dbh = DBI->connect("dbi:Sybase:server=BILLING",
                          $user, $passwd);

The default server is SYBASE, or the value of the $DSQUERY environment variable, if it is set.

database
Specify the database that should be made the default database. 
      $dbh = DBI->connect("dbi:Sybase:database=sybsystemprocs",
                          $user, $passwd);

This is equivalent to

     $dbh = DBI->connect('dbi:Sybase:', $user, $passwd);
     $dbh->do("use sybsystemprocs");
charset
Specify the character set that the client uses. 
      $dbh = DBI->connect("dbi:Sybase:charset=iso_1",
                          $user, $passwd);
language
Specify the language that the client uses. 
      $dbh = DBI->connect("dbi:Sybase:language=us_english",
                          $user, $passwd);

Note that the language has to have been installed on the server (via langinstall or sp_addlanguage) for this to work. If the language is not installed the session will default to the default language of the server.

packetSize
Specify the network packet size that the connection should use. Using a larger packet size can increase performance for certain types of queries. See the Sybase documentation on how to enable this feature on the server. 
      $dbh = DBI->connect("dbi:Sybase:packetSize=8192",
                          $user, $passwd);
interfaces
Specify the location of an alternate interfaces file: 
      $dbh = DBI->connect("dbi:Sybase:interfaces=/usr/local/sybase/interfaces",
                          $user, $passwd);
loginTimeout
Specify the number of seconds that DBI->connect() will wait for a response from the Sybase server. If the server fails to respond before the specified number of seconds the DBI->connect() call fails with a timeout error. The default value is 60 seconds, which is usually enough, but on a busy server it is sometimes necessary to increase this value: 
      $dbh = DBI->connect("dbi:Sybase:loginTimeout=240", # wait up to 4 minutes
                          $user, $passwd);
timeout
Specify the number of seconds after which any Open Client calls will timeout the connection and mark it as dead. Once a timeout error has been received on a connection it should be closed and re-opened for further processing.

Setting this value to 0 or a negative number will result in an unlimited timeout value. See also the Open Client documentation on CS_TIMEOUT.

      $dbh = DBI->connect("dbi:Sybase:timeout=240", # wait up to 4 minutes
                          $user, $passwd);
scriptName
Specify the name for this connection that will be displayed in sp_who (ie in the sysprocesses table in the program_name column). 
     $dbh->DBI->connect("dbi:Sybase:scriptName=myScript", $user, $password);
hostname
Specify the hostname that will be displayed by sp_who (and will be stored in the hostname column of sysprocesses).. 
     $dbh->DBI->connect("dbi:Sybase:hostname=kiruna", $user, $password);
tdsLevel
Specify the TDS protocol level to use when connecting to the server. Valid values are CS_TDS_40, CS_TDS_42, CS_TDS_46, CS_TDS_495 and CS_TDS_50. In general this is automatically negotiated between the client and the server, but in certain cases this may need to be forced to a lower level by the client. 
     $dbh->DBI->connect("dbi:Sybase:tdsLevel=CS_TDS_42", $user, $password);

NOTE: Setting the tdsLevel below CS_TDS_495 will disable a number of features, ?-style placeholders and CHAINED non-AutoCommit mode, in particular.

encryptPassword
Specify the use of the client password encryption supported by CT-Lib. Specify a value of 1 to use encrypted passwords. 
     $dbh->DBI->connect("dbi:Sybase:encryptPassword=1", $user, $password);

These different parameters (as well as the server name) can be strung together by separating each entry with a semi-colon:

     $dbh = DBI->connect("dbi:Sybase:server=ENGINEERING;packetSize=8192;language=us_english;charset=iso_1",
                         $user, $pwd);

Handling Multiple Result Sets

Sybase's Transact SQL has the ability to return multiple result sets from a single SQL statement. For example the query: 
     select b.title, b.author, s.amount
       from books b, sales s
      where s.authorID = b.authorID
      order by b.author, b.title
     compute sum(s.amount) by b.author

which lists sales by author and title and also computes the total sales by author returns two types of rows. The DBI spec doesn't really handle this situation, nor the more hairy

     exec my_proc @p1='this', @p2='that', @p3 out

where "my_proc" could return any number of result sets (ie it could perform an unknown number of "select" statements.

I've decided to handle this by returning an empty row at the end of each result set, and by setting a special Sybase attribute in $sth which you can check to see if there is more data to be fetched. The attribute is syb_more_results which you should check to see if you need to re-start the "fetch()" loop.

To make sure all results are fetched, the basic "fetch" loop can be written like this:

      do {
          while($d = $sth->fetch) {
             ... do something with the data
          }
      } while($sth->{syb_more_results});

You can get the type of the current result set with $sth->{syb_result_type}. This returns a numerical value, as defined in $SYBASE/include/cspublic.h:

         #define CS_ROW_RESULT           (CS_INT)4040
         #define CS_CURSOR_RESULT        (CS_INT)4041
         #define CS_PARAM_RESULT         (CS_INT)4042
         #define CS_STATUS_RESULT        (CS_INT)4043
         #define CS_MSG_RESULT           (CS_INT)4044
         #define CS_COMPUTE_RESULT       (CS_INT)4045

In particular, the return status of a stored procedure is returned as CS_STATUS_RESULT (4043), and is normally the last result set that is returned in a stored proc execution.

If you add a

     use DBD::Sybase;

to your script then you can use the symbolic values (CS_xxx_RESULT) instead of the numeric values in your programs, which should make them easier to read.

See also the "syb_output_param" func() call to handle stored procedures that only return OUTPUT parameters.

$sth->execute() failure mode behavior

THIS HAS CHANGED IN VERSION 0.21!

DBD::Sybase has the ability to handle multi-statement SQL commands in a single batch. For example, you could insert several rows in a single batch like this:

    $sth = $dbh->prepare("
    insert foo(one, two, three) values(1, 2, 3)
    insert foo(one, two, three) values(4, 5, 6)
    insert foo(one, two, three) values(10, 11, 12)
    insert foo(one, two, three) values(11, 12, 13)
    ");
    $sth->execute;

If anyone of the above inserts fails for any reason then $sth->execute will return "undef", HOWEVER the inserts that didn't fail will still be in the database, unless "AutoCommit" is off.

It's also possible to write a statement like this:

    $sth = $dbh->prepare("
    insert foo(one, two, three) values(1, 2, 3)
    select * from bar
    insert foo(one, two, three) values(10, 11, 12)
    ");
    $sth->execute;

If the second "insert" is the one that fails, then $sth->execute will NOT return "undef". The error will get flagged after the rows from "bar" have been fetched.

I know that this is not as intuitive as it could be, but I am constrained by the Sybase API here.

As an aside, I know that the example above doesn't really make sense, but I need to illustrate this particular sequence... You can also see the t/fail.t test script which shows this particular behavior.

Sybase Specific Attributes

There are a number of handle attributes that are specific to this driver. These attributes all start with syb_ so as to not clash with any normal DBI attributes.

Database Handle Attributes

The following Sybase specific attributes can be set at the Database handle level:

syb_show_sql (bool)
If set then the current statement is included in the string returned by $dbh->errstr.
syb_show_eed (bool)
If set, then extended error information is included in the string returned by $dbh->errstr. Extended error information include the index causing a duplicate insert to fail, for example.
syb_err_handler (subroutine ref)
This attribute is used to set an ad-hoc error handler callback (ie a perl subroutine) that gets called before the normal error handler does it's job. If this subroutine returns 0 then the error is ignored. This is useful for handling PRINT statements in Transact-SQL, for handling messages from the Backup Server, showplan output, dbcc output, etc.

The subroutine is called with nine parameters:

   o the Sybase error number
   o the severity
   o the state
   o the line number in the SQL batch
   o the server name (if available)
   o the stored procedure name (if available)
   o the message text
   o the current SQL command buffer
   o either of the strings "client" (for Client Library errors) or
     "server" (for server errors, such as SQL syntax errors, etc),
     allowing you to identify the error type.

As a contrived example, here is a port of the distinct error and message handlers from the Sybase documentation:

   Example:
   
   sub err_handler {
       my($err, $sev, $state, $line, $server,
         $proc, $msg, $sql, $err_type) = @_;
  
       my @msg = ();
       if($err_type eq 'server') {
          push @msg,
            ('',
             'Server message',
             sprintf('Message number: %ld, Severity %ld, State %ld, Line %ld',
                     $err,$sev,$state,$line),
             (defined($server) ? "Server '$server' " : '') .
             (defined($proc) ? "Procedure '$proc'" : ''),
             "Message String:$msg");
       } else {
          push @msg,
            ('',
             'Open Client Message:',
             sprintf('Message number: SEVERITY = (%ld) NUMBER = (%ld)',
                     $sev, $err),
             "Message String: $msg");
       }
       print STDERR join("\n",@msg);
       return 0; ## CS_SUCCEED
   }

In a simpler and more focused example, this error handler traps showplan messages:

    %showplan_msgs = map { $_ => 1}  (3612 .. 3615, 6201 .. 6299, 10201 .. 10299);
    sub err_handler {
       my($err, $sev, $state, $line, $server,
         $proc, $msg, $sql, $err_type) = @_;
   
        if($showplan_msgs{$err}) { # it's a showplan message
          print SHOWPLAN "$err - $msg\n";
          return 0;    # This is not an error
        }
        return 1;
    }

and this is how you would use it:

     $dbh = DBI->connect('dbi:Sybase:server=troll', 'sa', '');
     $dbh->{syb_err_handler} = \&err_handler;
     $dbh->do("set showplan on");
     open(SHOWPLAN, ">>/var/tmp/showplan.log") || die "Can't open showplan log: $!";
     $dbh->do("exec someproc");    # get the showplan trace for this proc.
     $dbh->disconnect;

NOTE - if you set the error handler in the DBI->connect() call like this

     $dbh = DBI->connect('dbi:Sybase:server=troll', 'sa', '', 
                     { syb_err_handler => \&err_handler });

then the err_handler() routine will get called if there is an error during
       the connect itself. This is new behavior in DBD::Sybase 0.95.

syb_flush_finish (bool)
If $dbh->{syb_flush_finish} is set then $dbh->finish will drain any results remaining for the current command by actually fetching them. The default behaviour is to issue a ct_cancel(CS_CANCEL_ALL), but this appears to cause connections to hang or to fail in certain cases (although I've never witnessed this myself.)
syb_dynamic_supported (bool)
This is a read-only attribute that returns TRUE if the dataserver you are connected to supports ?-style placeholders. Typically placeholders are not supported when using DBD::Sybase to connect to a MS-SQL server.
syb_chained_txn (bool)
If set then we use CHAINED transactions when AutoCommit is off. Otherwise we issue an explicit BEGIN TRAN as needed. The default is off.

This attribute should usually be used only during the connect() call:

     $dbh = DBI->connect('dbi:Sybase:', $user, $pwd, {syb_chained_txn => 1});

Using it at any other time with AutoCommit turned off will force a commit on the current handle.

syb_quoted_identifier (bool)
If set, then identifiers that would normally clash with Sybase reserved words can be quoted using "identifier". In this case strings must be quoted with the single quote.

Default is for this attribute to be off.

syb_rowcount (int)
Setting this attribute to non-0 will limit the number of rows returned by a SELECT, or affected by an UPDATE or DELETE statement to the rowcount value. Setting it back to 0 clears the limit.

Default is for this attribute to be 0.

syb_do_proc_status (bool)
Setting this attribute causes $sth->execute() to fetch the return status of any executed stored procs in the SQL being executed. If the return status is non-0 then $sth->execute() will report that the operation failed (ie it will return "undef"). This will NOT cause an error to be raised if RaiseError is set, however. To get that behaviour you need to generate a user error code in the stored proc via a 
     raiserror <num> <errmsg>

statement.

Setting this attribute does NOT affect existing $sth handles, only those that are created after setting it. To change the behavior of an existing $sth handle use $sth->{syb_do_proc_status}.

The default is for this attribute to be off.

syb_use_bin_0x
If set, BINARY and VARBINARY values are prefixed with '0x' in the result. The default is off.
syb_binary_images
If set, IMAGE data is returned in raw binary format. Otherwise the data is converted to a long hex string. The default is off.
syb_oc_version (string)
Returns the identification string of the version of Client Library that this binary is currently using. This is a read-only attribute.

For example:

     troll (7:59AM):348 > perl -MDBI -e '$dbh = DBI->connect("dbi:Sybase:", "sa"); print "$dbh->{syb_oc_version}\n";' 
     Sybase Client-Library/11.1.1/P/Linux Intel/Linux 2.2.5 i586/1/OPT/Mon Jun  7 07:50:21 1999

This is very useful information to have when reporting a problem.

syb_failed_db_fatal (bool)
If this is set, then a connect() request where the database specified doesn't exist or is not accessible will fail. This needs to be set in the attribute hash passed during the DBI->connect() call to be effective.

Default: off

syb_no_child_con (bool)
If this attribute is set then DBD::Sybase will not allow multiple simultaneously active statement handles on one database handle (i.e. multiple $dbh->prepare() calls without completely processing the results from any existing statement handle). This can be used to debug situations where incorrect or unexpected results are found due to the creation of a sub-connection where the connection attributes (in particular the current database) are different.

Default: off

syb_bind_empty_string_as_null (bool)
New in 0.95

If this attribute is set then an empty string (i.e. "") passed as a parameter to an $sth->execute() call will be converted to a NULL value. If the attribute is not set then an empty string is converted to a single space.

Default: off

syb_cancel_request_on_error (bool)
New in 0.95

If this attribute is set then a failure in a multi-statement request (for example, a stored procedure execution) will cause $sth->execute() to return failure, and will cause any other results from this request to be discarded.

The default value (on) changes the behavior that DBD::Sybase exhibited up to version 0.94.

Default: on

Statement Handle Attributes

The following read-only attributes are available at the statement level:

syb_more_results (bool)
See the discussion on handling multiple result sets above.
syb_result_type (int)
Returns the numeric result type of the current result set. Useful when executing stored procedurs to determine what type of information is currently fetchable (normal select rows, output parameters, status results, etc...).
syb_do_proc_status (bool)
See above (under Database Handle Attributes) for an explanation.
syb_no_bind_blob (bool)
If set then any IMAGE or TEXT columns in a query are NOT returned when calling $sth->fetch (or any variation).

Instead, you would use

     $sth->func($column, \$data, $size, 'ct_get_data');

to retrieve the IMAGE or TEXT data. If $size is 0 then the entire item is fetched, otherwis you can call this in a loop to fetch chunks of data:

     while(1) {
         $sth->func($column, \$data, 1024, 'ct_get_data');
         last unless $data;
         print OUT $data;
     }

The fetched data is still subject to Sybase's TEXTSIZE option (see the SET command in the Sybase reference manual). This can be manipulated with DBI's LongReadLen attribute, but "$dbh-"{LongReadLen}> must be set before $sth->execute() is called to take effect (note that LongReadLen has no effect when using DBD::Sybase with an MS-SQL server).

Note: The IMAGE or TEXT column that is to be fetched this way must be last in the select list.

See also the description of the ct_get_data() API call in the Sybase OpenClient manual, and the ``Working with TEXT/IMAGE columns'' section elsewhere in this document.

Controlling DATETIME output formats

By default DBD::Sybase will return DATETIME and SMALLDATETIME columns in the Nov 15 1998 11:13AM format. This can be changed via a special _date_fmt() function that is accessed via the $dbh->func() method.

The syntax is

     $dbh->func($fmt, '_date_fmt');

where $fmt is a string representing the format that you want to apply.

The formats are based on Sybase's standard conversion routines. The following subset of available formats has been implemented:

LONG
Nov 15 1998 11:30:11:496AM
SHORT
Nov 15 1998 11:30AM
DMY4_YYYY
15 Nov 1998
MDY1_YYYY
11/15/1998
DMY1_YYYY
15/11/1998
DMY2_YYYY
15.11.1998
YMD3_YYYY
19981115
HMS
11:30:11

Retrieving OUTPUT parameters from stored procedures

Sybase lets you pass define OUTPUT parameters to stored procedures, which are a little like parameters passed by reference in C (or perl.)

In Transact-SQL this is done like this

    declare @id_value int, @id_name char(10)
    exec my_proc @name = 'a string', @number = 1234, @id = @id_value OUTPUT, @out_name = @id_name OUTPUT
    -- Now @id_value and @id_name are set to whatever 'my_proc' set @id and @out_name to

So how can we get at @param using DBD::Sybase?

If your stored procedure only returns OUTPUT parameters, then you can use this shorthand:

     $sth = $dbh->prepare('...');
     $sth->execute;
     @results = $sth->func('syb_output_params');

This will return an array for all the OUTPUT parameters in the proc call, and will ignore any other results. The array will be undefined if there are no OUTPUT params, or if the stored procedure failed for some reason.

The more generic way looks like this:

    $sth = $dbh->prepare("declare \@id_value int, \@id_name
       exec my_proc @name = 'a string', @number = 1234, @id = @id_value OUTPUT, @out_name = @id_name OUTPUT");
    $sth->execute;
    do {
       while($d = $sth->fetch) {
          if($sth->{syb_result_type} == 4042) { # it's a PARAM result
             $id_value = $d->[0];
             $id_name  = $d->[1];
          }
       }
    } while($sth->{syb_more_results});

So the OUTPUT params are returned as one row in a special result set.

Multiple active statements on one $dbh

It is possible to open multiple active statements on a single database handle. This is done by opening a new physical connection in $dbh->prepare() if there is already an active statement handle for this $dbh.

This feature has been implemented to improve compatibility with other drivers, but should not be used if you are coding directly to the Sybase driver.

If AutoCommit is OFF then multiple statement handles on a single $dbh is NOT supported. This is to avoid various deadlock problems that can crop up in this situation, and because you will not get real transactional integrity using multiple statement handles simultaneously as these in reality refer to different physical connections.

Working with IMAGE and TEXT columns

DBD::Sybase can store and retrieve IMAGE or TEXT data (aka ``blob'' data) via standard SQL statements. The LongReadLen handle attribute controls the maximum size of IMAGE or TEXT data being returned for each data element.

When using standard SQL the default for IMAGE data is to be converted to a hex string, but you can use the syb_binary_images handle attribute to change this behaviour. Alternatively you can use something like

     $binary = pack("H*", $hex_string);

to do the conversion.

IMAGE and TEXT datatypes can not be passed as parameters using ?-style placeholders, and placeholders can't refer to IMAGE or TEXT columns (this is a limitation of the TDS protocol used by Sybase, not a DBD::Sybase limitation.)

There is an alternative way to access and update IMAGE/TEXT data using the natice OpenClient API. This is done via $h->func() calls, and is, unfortunately, a little convoluted.

Handling IMAGE/TEXT data with ct_get_data()/ct_send_data()

$len = ct_fetch_data($col, $dataref, $numbytes)
The ct_get_data() call allows you to fetch IMAGE/TEXT data in raw format, either in one piece or in chunks. To use this function you must set the syb_no_bind_blob statement handle to TRUE.

ct_get_data() takes 3 parameters: The column number (starting at 1) of the query, a scalar ref and a byte count. If the byte count is 0 then we read as many bytes as possible.

Note that the IMAGE/TEXT column must be last in the select list for this to work.

The call sequence is:

     $sth = $dbh->prepare("select id, img from some_table where id = 1");
     $sth->{syb_no_bind_blob} = 1;
     $sth->execute;
     while($d = $sth->fetchrow_arrayref) {
        # The data is in the second column
        $len = $sth->func(2, \$img, 0, 'ct_get_data');
     }

ct_get_data() returns the number of bytes that were effectively fetched, so that when fetching chunks you can do something like this:

    while(1) {
       $len = $sth->func(2, $imgchunk, 1024, 'ct_get_data');
       ... do something with the $imgchunk ...
       last if $len != 1024;
    }

To explain further: Sybase stores IMAGE/TEXT data separately from normal table data, in a chain of 2k blocks. To update an IMAGE/TEXT column Sybase needs to find the head of this chain, which is known as the ``text pointer''. As there is no where clause when the ct_send_data() API is used we need to retrieve the text pointer for the correct data item first, which is done via the ct_data_info(CS_GET) call. Subsequent ct_send_data() calls will then know which data item to update.

$status = ct_data_info($action, $column, $attr)
ct_data_info() is used to fetch or update the CS_IODESC structure for the IMAGE/TEXT data item that you wish to update. $action should be one of ``CS_SET'' or ``CS_GET'', $column is the column number of the active select statement (ignored for a CS_SET operation) and $attr is a hash ref used to set the values in the struct.

ct_data_info() must be first called with CS_GET to fetch the CS_IODESC structure for the IMAGE/TEXT data item that you wish to update. Then you must update the value of the total_txtlen structure element to the length (in bytes) of the IMAGE/TEXT data that you are going to insert, and optionally set the log_on_update to TRUE to enable full logging of the operation.

ct_data_info(CS_GET) will fail if the IMAGE/TEXT data for which the CS_IODESC is being fetched is NULL. If you have a NULL value that needs updating you must first update it to some non-NULL value (for example an empty string) using standard SQL before you can retrieve the CS_IODESC entry. This actually makes sense because as long as the data item is NULL there is no text pointer and no TEXT page chain for that item.

See the ct_send_data() entry below for an example.

ct_prepare_send()
ct_prepare_send() must be called to initialize a IMAGE/TEXT write operation. See the ct_send_data() entry below for an example.
ct_finish_send()
ct_finish_send() is called to finish/commit an IMAGE/TEXT write operation. See the ct_send_data() entry below for an example.
ct_send_data($image, $bytes)
Send $bytes bytes of $image to the database. The request must have been set up via ct_prepare_send() and ct_data_info() for this to work. ct_send_data() returns TRUE on success, and FALSE on failure.

In this example, we wish to update the data in the img column where the id column is 1:

   # first we need to find the CS_IODESC data for the data
   $sth = $dbh->prepare("select img from imgtable where id = 1");
   $sth->execute;
   while($sth->fetch) {    # don't care about the data!
       $sth->func('CS_GET', 1, 'ct_data_info');
   }
 
   # OK - we have the CS_IODESC values, so do the update:
   $sth->func('ct_prepare_send');
   # Set the size of the new data item (that we are inserting), and make
   # the operation unlogged
   $sth->func('CS_SET', 1, {total_txtlen => length($image), log_on_update => 0}, 'ct_data_info');
   # now transfer the data (in a single chunk, this time)
   $sth->func($image, length($image), 'ct_send_data');
   # commit the operation
   $sth->func('ct_finish_send');

The ct_send_data() call can also transfer the data in chunks, however you must know the total size of the image before you start the insert. For example:

   # update a database entry with a new version of a file:
   my $size = -s $file;
   # first we need to find the CS_IODESC data for the data
   $sth = $dbh->prepare("select img from imgtable where id = 1");
   $sth->execute;
   while($sth->fetch) {    # don't care about the data!
       $sth->func('CS_GET', 1, 'ct_data_info');
   }
 
   # OK - we have the CS_IODESC values, so do the update:
   $sth->func('ct_prepare_send');
   # Set the size of the new data item (that we are inserting), and make
   # the operation unlogged
   $sth->func('CS_SET', 1, {total_txtlen => $size, log_on_update => 0}, 'ct_data_info');
 
   # open the file, and store it in the db in 1024 byte chunks.
   open(IN, $file) || die "Can't open $file: $!";
   while($size) {
       $to_read = $size > 1024 ? 1024 : $size;
       $bytesread = read(IN, $buff, $to_read);
       $size -= $bytesread;
 
       $sth->func($buff, $bytesread, 'ct_send_data');
   }
   close(IN);
   # commit the operation
   $sth->func('ct_finish_send');

AutoCommit, Transactions and Transact-SQL

When $h->{AutoCommit} is off all data modification SQL statements that you issue (insert/update/delete) will only take effect if you call $dbh->commit.

DBD::Sybase implements this via two distinct methods, depending on the setting of the $h->{syb_chained_txn} attribute and the version of the server that is being accessed.

If $h->{syb_chained_txn} is off, then the DBD::Sybase driver will send a BEGIN TRAN before the first $dbh->prepare(), and after each call to $dbh->commit() or $dbh->rollback(). This works fine, but will cause any SQL that contains any CREATE TABLE (or other DDL) statements to fail. These CREATE TABLE statements can be burried in a stored procedure somewhere (for example, "sp_helprotect" creates two temp tables when it is run). You can get around this limit by setting the "ddl in tran" option (at the database level, via "sp_dboption".) You should be aware that this can have serious effects on performance as this causes locks to be held on certain system tables for the duration of the transaction.

If $h->{syb_chained_txn} is on, then DBD::Sybase sets the CHAINED option, which tells Sybase not to commit anything automatically. Again, you will need to call $dbh->commit() to make any changes to the data permanent. In this case Sybase will not let you issue BEGIN TRAN statements in the SQL code that is executed, so if you need to execute stored procedures that have BEGIN TRAN statements in them you must use $h->{syb_chained_txn} = 0, or $h->{AutoCommit} = 1.

Using ? Placeholders & bind parameters to $sth->execute

DBD::Sybase supports the use of ? placeholders in SQL statements as long as the underlying library and database engine supports it. It does this by using what Sybase calls Dynamic SQL. The ? placeholders allow you to write something like: 
         $sth = $dbh->prepare("select * from employee where empno = ?");
 
         # Retrieve rows from employee where empno == 1024:
         $sth->execute(1024);
         while($data = $sth->fetch) {
             print "@$data\n";
         }
 
        # Now get rows where empno = 2000:
         
         $sth->execute(2000);
         while($data = $sth->fetch) {
             print "@$data\n";
         }

When you use ? placeholders Sybase goes and creates a temporary stored procedure that corresponds to your SQL statement. You then pass variables to $sth->execute or $dbh->do, which get inserted in the query, and any rows are returned.

DBD::Sybase uses the underlying Sybase API calls to handle ?-style placeholders. For select/insert/update/delete statements DBD::Sybase calls the ct_dynamic() family of Client Library functions, which gives DBD::Sybase data type information for each parameter to the query.

You can only use ?-style placeholders for statements that return a single result set, and the ? placeholders can only appear in a WHERE clause, in the SET clause of an UPDATE statement, or in the VALUES list of an INSERT statement.

The DBI docs mention the following regarding NULL values and placeholders:

        Binding an `undef' (NULL) to the placeholder will not
        select rows which have a NULL `product_code'! Refer to the
        SQL manual for your database engine or any SQL book for
        the reasons for this.  To explicitly select NULLs you have
        to say "`WHERE product_code IS NULL'" and to make that
        general you have to say:
 
          ... WHERE (product_code = ? OR (? IS NULL AND product_code IS NULL))
 
        and bind the same value to both placeholders.

This will not work with a Sybase database server. If you attempt the above construct you will get the following error:

The datatype of a parameter marker used in the dynamic prepare statement could not be resolved.

The specific problem here is that when using ? placeholders the prepare() operation is sent to the database server for parameter resoltion. This extracts the datatypes for each of the placeholders. Unfortunately the "? is null" construct doesn't tie the ? placeholder with an existing table column, so the database server can't find the data type. As this entire operation happens inside the Sybase libraries there is no easy way for DBD::Sybase to work around it.

Note that Sybase will normally handle the "foo = NULL" construct the same way that other systems handle "foo is NULL", so the convoluted construct that is described above is not necessary to obtain the correct results when querying a Sybase database.

The underlying API does not support ?-style placeholders for stored procedures, but see the section on titled Stored Procedures and Placeholders elsewhere in this document.

?-style placeholders can NOT be used to pass TEXT or IMAGE data items to the server. This is a limitation of the TDS protocol, not of DBD::Sybase.

There is also a performance issue: OpenClient creates stored procedures in tempdb for each prepare() call that includes ? placeholders. Creating these objects requires updating system tables in the tempdb database, and can therefore create a performance hotspot if a lot of prepare() statements from multiple clients are executed simultaneously. This problem has been corrected for Sybase 11.9.x and later servers, as they create ``lightweight'' temporary stored procs which are held in the server memory cache and don't affect the system tables at all.

In general however I find that if your application is going to run against Sybase it is better to write ad-hoc stored procedures rather than use the ? placeholders in embedded SQL.

Out of curiosity I did some simple timings to see what the overhead of doing a prepare with ? placehoders is vs. a straight SQL prepare and vs. a stored procedure prepare. Against an 11.0.3.3 server (linux) the placeholder prepare is significantly slower, and you need to do ~30 execute() calls on the prepared statement to make up for the overhead. Against a 12.0 server (solaris) however the situation was very different, with placeholder prepare() calls slightly faster than straight SQL prepare(). This is something that I really don't understand, but the numbers were pretty clear.

In all cases stored proc prepare() calls were clearly faster, and consistently so.

This test did not try to gauge concurrency issues, however.

It is not possible to retrieve the last IDENTITY value after an insert done with ?-style placeholders. This is a Sybase limitation/bug, not a DBD::Sybase problem. For example, assuming table foo has an identity column:

   $dbh->do("insert foo(col1, col2) values(?, ?)", undef, "string1", "string2");
   $sth = $dbh->prepare('select @@identity') 
     || die "Can't prepare the SQL statement: $DBI::errstr";
   $sth->execute || die "Can't execute the SQL statement: $DBI::errstr";
 
   #Get the data back.
   while (my $row = $sth->fetchrow_arrayref()) {
     print "IDENTITY value = $row->[0]\n";
   }

will always return an identity value of 0, which is obviously incorrect. This behaviour is due to the fact that the handling of ?-style placeholders is implemented using temporary stored procedures in Sybase, and the value of @@identity is reset when the stored procedure has executed. Using an explicit stored procedure to do the insert and trying to retrieve @@identity after it has executed results in the same behaviour.

Please see the discussion on Dynamic SQL in the OpenClient C Programmer's Guide for details. The guide is available on-line at http://sybooks.sybase.com/

Stored Procedures and Placeholders

NOTE: This feature is experimental

This version of DBD::Sybase introduces the ability to use ?-style placeholders as parameters to stored proc calls. The requirements are that the stored procedure call be initiated with an ``exec'' and that it be the only statement in the batch that is being prepared():

For example, this prepares a stored proc call with named parameters:

     my $sth = $dbh->prepare("exec my_proc \@p1 = ?, \@p2 = ?");
     $sth->execute('one', 'two');

You can also use positional parameters:

     my $sth = $dbh->prepare("exec my_proc ?, ?");
     $sth->execute('one', 'two');

You may not mix positional and named parameter in the same prepare.

You can specify OUTPUT parameters in the usual way, but you can NOT use bind_param_inout() to get the output result - instead you have to call fetch() and/or $sth->func('syb_output_params'):

     my $sth = $dbh->prepare("exec my_proc \@p1 = ?, \@p2 = ?, \@p3 = ? OUTPUT ");
     $sth->execute('one', 'two', 'three');
     my (@data) = $sth->func('syb_output_params');

DBD::Sybase does not attempt to figure out the correct parameter type for each parameter (it would be possible to do this for most cases, but there are enough exceptions that I preferred to avoid the issue for the time being). DBD::Sybase defaults all the parameters to SQL_CHAR, and you have to use bind_param() with an explicit type value to set this to something different. The type is then remembered, so you only need to use the explicit call once for each parameter:

     my $sth = $dbh->prepare("exec my_proc \@p1 = ?, \@p2 = ?");
     $sth->bind_param(1, 'one', SQL_CHAR);
     $sth->bind_param(2, 2.34, SQL_FLOAT);
     $sth->execute;
     ....
     $sth->execute('two', 3.456);
     etc...

When binding SQL_NUMERIC or SQL_DECIMAL data you may get fatal conversion errors if the scale or the precision exceeds the size of the target parameter definition.

For example, consider the following stored proc definition:

     declare proc my_proc @p1 numeric(5,2) as...

and the following prepare/execute snippet:

     my $sth = $dbh->prepare("exec my_proc \@p1 = ?");
     $sth->bind_param(1, 3.456, SQL_NUMERIC);

This generates the following error:

DBD::Sybase::st execute failed: Server message number=241 severity=16 state=2 line=0 procedure=dbitest text=Scale error during implicit conversion of NUMERIC value '3.456' to a NUMERIC field.

You can tell Sybase (and DBD::Sybase) to ignore these sorts of errors by setting the arithabort option:

     $dbh->do("set arithabort off");

See the set command in the Sybase Adaptive Server Enterprise Reference Manual for more information on the set command and on the arithabort option.

BUGS

You can run out of space in the tempdb database if you use a lot of calls with bind variables (ie ?-style placeholders) without closing the connection. On my system, with an 8 MB tempdb database I run out of space after 760 prepare() statements with ?-parameters. This is because Sybase creates stored procedures for each prepare() call. So my suggestion is to only use ?-style placeholders if you really need them (i.e. if you are going to execute the same prepared statement multiple times).

The new primary_key_info() method will only return data for tables where a declarative ``primary key'' constraint was included when the table was created.

I have a simple bug tracking database at http://www.peppler.org/cgi-bin/bug.cgi . You can use it to view known problems, or to report new ones. Keep in mind that peppler.org is connected to the net via a K56 dialup line, so it may be slow.

Using DBD::Sybase with MS-SQL

MS-SQL started out as Sybase 4.2, and there are still a lot of similarities between Sybase and MS-SQL which makes it possible to use DBD::Sybase to query a MS-SQL dataserver using either the Sybase OpenClient libraries or the FreeTDS libraries (see http://www.freetds.org).

However, using the Sybase libraries to query an MS-SQL server has certain limitations. In particular ?-style placeholders are not supported (although support when using the FreeTDS libraries is possible in a future release of the libraries), and certain syb_ attributes may not be supported.

Sybase defaults the TEXTSIZE attribute (aka LongReadLen) to 32k, but MS-SQL 7 doesn't seem to do that correctly, resulting in very large memory requests when querying tables with TEXT/IMAGE data columns. The work-around is to set TEXTSIZE to some decent value via $dbh->{LongReadLen} (if that works - I haven't had any confirmation that it does) or via $dbh->do(``set textsize <somesize>'');

nsql

The nsql() call is a direct port of the function of the same name that exists in Sybase::DBlib.

Usage:

    @data = $dbh->func($sql, $type, $callback, 'nsql');

This executes the query in $sql, and returns all the data in @data. The $type parameter can be used to specify that each returned row be in array form (i.e. $type passed as 'ARRAY', which is the default) or in hash form ($type passed as 'HASH') with column names as keys.

If $callback is specified it is taken as a reference to a perl sub, and each row returned by the query is passed to this subroutine instead of being returned by the routine (to allow processing of large result sets, for example).

"nsql" also checks three special attributes to enable deadlock retry logic \(Note none of these attributes have any effect anywhere else at the moment):

syb_deadlock_retry count
Set this to a non-0 value to enable deadlock detection and retry logic within nsql(). If a deadlock error is detected (error code 1205) then the entire batch is re-submitted up to syb_deadlock_retry times. Default is 0 (off).
syb_deadlock_sleep seconds
Number of seconds to sleep between deadlock retries. Default is 60.
syb_deadlock_verbose (bool)
Enable verbose logging of deadlock retry logic. Default is off.

Deadlock detection will be added to the $dbh->do() method in a future version of DBD::Sybase.

SEE ALSO

DBI

Sybase OpenClient C manuals.

Sybase Transact SQL manuals.

AUTHOR

DBD::Sybase by Michael Peppler The DBD::Sybase module is Copyright (c) 1997-2003 Michael Peppler. The DBD::Sybase module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

ACKNOWLEDGEMENTS

Tim Bunce for DBI, obviously!

See also ``ACKNOWLEDGEMENTS'' in DBI.