NAME

DBD::Informix - Access to Informix Databases

SYNOPSIS

use DBI;

DESCRIPTION

This document describes Informix Database Driver for Perl Version 0.97005 (2000-02-10).

You should also read the documentation for DBI perldoc DBI as this document qualifies what is stated there. Note that this document was last fully updated for the DBI Version 0.85 specification, but the code requires features from DBI Version 1.02 and is normally built with DBI Version 1.13. Consequently, both this document and DBD::Informix are probably considerably out of line with some of the new features and minor details of the DBI specification.

This document still has a biased view of how to use DBI and DBD::Informix and covers parts of DBI and most of DBD::Informix. In late 1996, the DBI documentation was in a very confused state. The DBI documentation has improved with each release of DBI, and the comments in the DBI document about DBI and its drivers are a better indication of what should happen. However, this document might still be a better reflection of the actual behavior of DBD::Informix.

Be aware that on occasion, the description in this document gets complex because of differences between different versions of Informix software and different types of Informix databases. The key factor is the version of ESQL/C used when building DBD::Informix. Basically, there are two groups of versions to worry about, the 5.0x family of versions (5.00.UC1 through 5.10.UCx at the moment), and the 6.0x and later family of versions (6.00.UE1 through 9.30.UCx at the moment). All version families acquire extra versions on occasion.

Note that DBD::Informix does not work with Informix ESQL/C Version 4.1x or earlier versions because it uses both SQL descriptors and strings for cursor names and statement names, and these features were not available before Version 5.00.

For information about Informix software, you should also read the Notes/Informix.License file that is distributed with DBD::Informix.

For a Japanese translation of a recent version of this documentation (maintained by Kawai Takanori <kawai@nippon-rad.co.jp>), see the following Web site:

http://member.nifty.ne.jp/hippo2000/perltips/DBD/informix.htm

USE OF DBD::Informix

LOADING DBD::Informix

To use the DBD::Informix software, you need to load the DBI software.

use DBI;

Under normal circumstances, you should then connect to your database using the notation in the section "CONNECTING TO A DATABASE," which calls DBI->connect(). Note that some of the DBD::Informix test code does not operate under normal circumstances and therefore uses the nonpreferred techniques in the section "Driver Attributes and Methods."

Note that you do not write:

use DBD::Informix;      # !!BUGGY CODE!!

DRIVER ATTRIBUTES AND METHODS

If you have a burning desire to explicitly install the Informix driver independently of connecting to any database, use:

$drh = DBI->install_driver('Informix');

This statement gives you a reference to the driver, also known as the driver handle. If the load fails, your program stops immediately (unless, perhaps, you eval the statement).

Once you have the driver handle, you can interrogate the driver for some basic information:

print "Driver Information\n";
# Type is always 'dr'.
print "    Type:                  $drh->{Type}\n";
# Name is always 'Informix'.
print "    Name:                  $drh->{Name}\n";
# Version is the version of DBD::Informix (such as 0.51).
print "    Version:               $drh->{Version}\n";
# The Attribution identifies the culprits who provided you
# with this software.
print "    Attribution:           $drh->{Attribution}\n";
# ProductName is the version of ESQL/C; it corresponds to
# the first line of the output from "esql -V".
print "    Product:               $drh->{ix_ProductName}\n";
# ProductVersion is an integer version number such as 721
# for ESQL/C Version 7.21.UC1.
print "    Product Version:       $drh->{ix_ProductVersion}\n";
# MultipleConnections indicates whether the driver
# supports multiple connections (1) or not (0).
print "    Multiple Connections:  $drh->{ix_MultipleConnections}\n";
# ActiveConnections identifies the number of open connections.
print "    Active Connections:      $drh->{ix_ActiveConnections}\n";
# CurrentConnection identifies the current connection.
print "    Current Connections:     $drh->{ix_CurrentConnection}\n";

Once you have loaded the driver, you can connect to a database, or you can sever all connections to databases with disconnect_all.

$drh->disconnect_all;

To find out which databases are available, you can use the function:

@dbnames = DBI->data_sources('Informix');

Note that you might also be able to connect to other databases not listed by DBI->datasources using other notations to identify the database. For example, you can connect to "dbase@server" if "server" appears in the sqlhosts file and the database "dbase" exists on the server and the server is up and you have permission to use both the server and the database on the server and so on. Also, you might not be able to connect to every one of the databases listed if you have not been given at least connect permission on the database. However, the databases listed by the DBI->data_sources method certainly exist, and it is legitimate to try connecting to those sources.

You can test whether this worked with:

if (defined @dbnames) { ...process array... }
else                  { ...process error... }

CONNECTING TO A DATABASE

To connect to a database, you can use the connect function, which yields a valid reference or database handle if it is successful. If the driver itself cannot be loaded (by the DBI->install_driver() method mentioned above), DBI aborts the script (and DBD::Informix can do nothing about it because it was not loaded successfully).

In versions of DBD::Informix prior to Version 1.00 (except for Version 0.62), you get a warning if INFORMIXDIR is not set in the environment; you can only suppress that warning by setting INFORMIXDIR. In Versions 0.62 and 1.00 or later, the default value for INFORMIXDIR is recorded when DBD::Informix is built and INFORMIXDIR is set at run time if no value is inherited in the environment. This is of most value to web-based applications. Similarly, INFORMIXSERVER is recorded when DBD::Informix is built and set at run time if no value is inherited in the environment. Note that prior to Version 0.95, you needed to set LD_LIBRARY_PATH or the local equivalent (such as SHLIB_PATH) before trying to load the DBD::Informix driver. By default, DBD::Informix Version 0.95 and later is built with absolute path names for the shared libraries and the setting of LD_LIBRARY_PATH is not critical unless you overrode the default with DBD_INFORMIX_RELOCATABLE_INFORMIXDIR.

$dbh = DBI->connect("dbi:Informix:$database");
$dbh = DBI->connect("dbi:Informix:$database", $user, $pass);
$dbh = DBI->connect("dbi:Informix:$database", $user, $pass, %attr);

The DBI connect method strips the 'dbi:' prefix from the first argument and loads the DBD module identified by the next string (Informix in this case). The string following the second colon is all that is passed to the DBD::Informix code. With this format, you do not have to specify the username or password. Note that if you specify the username but not the password, DBD::Informix will silently ignore the username. You can also specify certain attributes in the connect call. These attributes include:

AutoCommit
PrintError
RaiseError

Note that you cannot specify ChopBlanks in this list. DBD::Informix formerly recognized the ix_AutoErrorReport attribute as a synonym for the PrintError attribute, except that ix_AutoErrorReport was not recognized in the connect call. However, because ix_AutoErrorReport now generates a warning and is otherwise ignored, you should upgrade any code that uses it to use the standard DBI attribute PrintError instead. If you use the new style connect, you could therefore specify that the database is not to operate in AutoCommit mode, but errors should be reported automatically by specifying:

$dbh = DBI->connect("dbi:Informix:$database", '', '',
                    { AutoCommit => 0, PrintError => 1 });

With this style of connection, the default value for AutoCommit is On (or 1); this is a contrast to the old style where the default is Off (or 0). Note also that starting with DBD::Informix Version 0.56, the behavior is not affected by the type of Informix database to which you are connecting, except that you might get a warning if you try to set AutoCommit Off when you connect to an UnLogged database. See also the extensive notes in the TRANSACTION MANAGEMENT section later in this document.

OBSOLESCENT CONNECTION METHOD

The older style of connection does not use the string "dbi:Informix:" at the start of the first argument. This style is strongly deprecated, notwithstanding the fact that one of the tests uses it.

$dbh = DBI->connect($database, $username, $password, 'Informix');

Note that if you omit the fourth argument ('Informix'), DBI loads any driver it chooses according to its rules; the actual driver loaded is not controlled by DBD::Informix. If you omit the fourth argument, you can also omit the $password and $username arguments. If you specify the fourth argument, you can leave the $password and $username arguments empty, and they will be ignored.

$dbh = DBI->connect($database, $username, $password);
$dbh = DBI->connect($database, $username);
$dbh = DBI->connect($database);

INFORMIX CONNECTION SEMANTICS

If you are using ESQL/C Versions 5.x, DBD::Informix ignores the username and password data, and the statement is equivalent to "EXEC SQL DATABASE :database;". If you are using ESQL/C Versions 6.0x or later, DBD::Informix uses the username and password only if both are supplied, but it is then equivalent to:

EXEC SQL CONNECT TO :database AS :connection
    USER :username USING :password
    WITH CONCURRENT TRANSACTIONS

DBD::Informix gives the connection a name.

For DBD::Informix, the database name is any valid format for the DATABASE or CONNECT statements.

Valid database names include the following examples:

dbase               # 'Local' database
//machine1/dbase    # Database on remote machine
dbase@server1       # Database on (remote) server (as defined in sqlhosts)
@server1            # Connection to (remote) server but no database
/some/where/dbase   # Connect to local SE database

No database name is supplied implicitly by DBD::Informix (though the test code in DBD::Informix::TestHarness does supply the names of test databases implicitly). Read the DBI driver documentation to see what, if any, defaults will be supplied (for example, check for the DBI_DRIVER and DBI_DSN environment variables). If DBD::Informix sees an empty string, it makes no connection to any database with ESQL/C 5.0x, and it makes a default connection with ESQL/C 6.00 and later. An additional string, ".DEFAULT.", can be specified explicitly as the database name and will be interpreted as a request for a default connection. Note that this string is not a valid Informix database name, so there can be no confusion.

Once you have a database handle, you can interrogate it for some basic information about the database. The ix_ServerVersion, ix_BlobSupport, and ix_StoredProcedures attributes are read-only attributes. They were introduced in DBD::Informix Version 0.95 mainly to provide support for the XPS servers, which do not necessarily have blob and stored procedure support, unlike other versions of Informix OnLine. Note that to determine these values, DBD::Informix interrogates the system catalog, which represents a small performance hit. The server version number is retrieved from the entry in "informix".systables with the table name 'bVERSION' (where the b represents a blank). It is not always precisely the version that is reported by the oninit program, for example, but the difference is usually small and not critical. DBD::Informix cannot use the Informix utilitess to determine the database version more accurately because there is no guarantee that the database server is on the same machine as the DBD::Informix code.

print "Database Information\n";
# Type is always 'db'.
print "    Type:                    $dbh->{Type}\n";
# ix_ServerVersion is a number, just like ix_ProductVersion is a number.
# Although Version 5.10.UC7 SE servers correctly report a
# version number, some earlier versions might report 0.
print "    Server Version:          $dbh->{ix_ServerVersion}\n";
# Name is the name of the database specified at connect.
print "    Original Database Name:  $dbh->{Name}\n";
# ix_DatabaseName is the name of the current database.
print "    Current Database Name:   $dbh->{ix_DatabaseName}\n";
# AutoCommit is 1 (true) if the database commits each statement.
print "    AutoCommit:              $dbh->{AutoCommit}\n";

# ix_InformixOnLine is 1 (true) if the handle is connected to an
# Informix-OnLine server.
print "    Informix-OnLine:         $dbh->{ix_InformixOnLine}\n";
# ix_LoggedDatabase is 1 (true) if the database has
# transactions.
print "    Logged Database:         $dbh->{ix_LoggedDatabase}\n";
# ix_ModeAnsiDatabase is 1 (true) if the database is MODE ANSI.
print "    Mode ANSI Database:      $dbh->{ix_ModeAnsiDatabase}\n";
# PrintError is 1 (true) if errors are reported when detected.
print "    Print Errors:            $dbh->{PrintError}\n";
# ix_InTransaction is 1 (true) if the database is in a transaction.
print "    Transaction Active:      $dbh->{ix_InTransaction}\n";
# ix_BlobSupport is 1 (true) if the database supports blobs.
print "    Blob Support:            $dbh->{ix_BlobSupport}\n";
# ix_StoredProcedures is 1 (true) if the database has stored procedures.
print "    Stored Procedures:       $dbh->{ix_StoredProcedures}\n";
# ix_ConnectionName is the name of the ESQL/C connection.
# Mainly applicable with Informix ESQL/C 6.00 and later.
print "    Connection Name:         $dbh->{ix_ConnectionName}\n";

If $dbh->{PrintError} is true, then DBI will report each error automatically on STDERR when it is detected. The error is also available via the package variables $DBI::errstr and $DBI::err. Note that $DBI::errstr includes the SQL error number and the ISAM error number if there is one. The message might extend over several lines and is generally formatted so that it can be displayed neatly within 80 columns. The last character of the message used to be a newline, but starting with Version 0.62, the trailing new line is omitted to improve the automatic error reports from Perl.

If $dbh->{PrintError} is false, then DBI does not report any errors when it detects them; the user must note that errors have occurred and decide whether to report them.

If you connect using the DBI->connect() method, or if you have forgotten the driver, you can discover it again using:

$drh = $dbh->{Driver};

This statement allows you to access the driver methods and attributes described previously.

Starting with Version 0.60, the name of the database is now tracked accurately when the DATABASE, CLOSE DATABASE, CREATE DATABASE, ROLLFORWARD DATABASE, and START DATABASE statements are used. Note that you cannot prepare CONNECT statements, so they do not have to be tracked.

METADATA

You can call two methods using the DBI func() to get at some basic Informix metadata relatively conveniently.

@list = $dbh->func('_tables');
@list = $dbh->func('user', '_tables');
@list = $dbh->func('base', '_tables');
@list = $dbh->func('user', 'base', '_tables');
@list = $dbh->func('system', '_tables');
@list = $dbh->func('view', '_tables');
@list = $dbh->func('synonym', '_tables');

The lists of tables are all qualified as "owner".tablename, and you can use them in SQL statements without fear that the table is not present in the database (unless someone deletes it behind your back). The leading arguments qualify the list of names returned. Private synonyms are reported for just the current user.

@list = $dbh->func('_columns');
@list = $dbh->func(@tables, '_columns');

The lists are each references to an array of values corresponding to the owner name, table name, column number, column name, basic data type (ix_ColType value--see below), and data length (ix_ColLength--see below). If no tables are listed, all columns in the database are listed. This can be quite slow because handling synonyms properly requires a UNION operation. Further, although the '_tables' method reports the names of remote synonyms, the '_columns' method does not expand them (mainly because it is very hard to do properly). See the examples in t/t55mdata.t for how to use these methods. Exercise for the reader: Extend '_columns' to get reports on the columns in remote synonyms, including relocated remote synonyms where the original referenced site now forwards the name to a third site!

DISCONNECTING FROM A DATABASE

You can also disconnect from the database:

$dbh->disconnect;

The previous example will roll back any uncommitted work. Note that this example does not destroy the database handle. You need to do an explicit 'undef $dbh' to destroy the handle. Any statements you prepare with this handle are finished (see below) and cannot be used again. All space associated with the statements is released.

If you are using an Informix driver for which $drh->{ProductVersion} >= 600, you can have multiple concurrent connections (subject to the normal Informix constraint that a single process can have at most one shared memory connection open at any time). This means that multiple calls to $drh->connect will give you independent connections to one or more databases.

If you are using an Informix driver for which $drh->{ProductVersion} < 600, you cannot have multiple concurrent connections. If you make multiple calls to $drh->connect, you will achieve the same effect as if you execute several database statements in a row. Multiple calls to $drh->connect will generally switch databases successfully but will invalidate any statements you previously prepared. Multiple calls to $drh->connect might fail in instances when the current database is not local or when there is an active transaction.

SIMPLE STATEMENTS

Given a database connection, you can execute a variety of simple statements with a variety of different calls:

$dbh->commit;
$dbh->rollback;

These two operations commit or roll back the current transaction. If the database is unlogged, the two operations do nothing. If AutoCommit is set to 1, the two operations do nothing useful. If AutoCommit is set to 0, a new transaction is started (implicitly for a database that is MODE ANSI, explicitly for a database that is not MODE ANSI).

To execute most preparable parameterless statements you can use:

$dbh->do($stmt);

The statement must be neither a SELECT statement other than SELECT...INTO TEMP nor an EXECUTE PROCEDURE statement where the procedure returns data.

You can execute an arbitrary statement with parameters using:

$dbh->do($stmt, undef, @parameters);
$dbh->do($stmt, undef, $param1, $param2);

The 'undef' represents an undefined reference to a hash of attributes (\%attr) that is documented in the DBI specification. The Version 0.56 edition of this documentation omitted this argument and caused confusion. Again, the statement must not be a SELECT or EXECUTE PROCEDURE that returns data. The values in @parameters (or the separate values) are bound to the question marks in the statement string.

$sth = $dbh->prepare($stmt);
$sth->execute(@parameters);

The code in DBD::Informix Versions 0.26 through 0.55 handled the 'do' operation exclusively with its own code and used the EXECUTE IMMEDIATE statement when possible. Releases prior to 0.26 and releases from 0.56 onwards use the code from the DBI package and do not use EXECUTE IMMEDIATE.

The only reliable way to embed an arbitrary string inside a statement is to use the quote method:

$dbh->quote($string);

This method is provided by the DBI package implementation and is inherited by the DBD::Informix package. The string is enclosed in single quotes, and any embedded single quotes are doubled up, which conforms to the SQL-92 standard. You might typically use this method in a context such as:

$value = q{Doesn't work unless quotes ("'" and '"') are handled};

$stmt = "INSERT INTO SomeTable(SomeColumn) " .
        "VALUES(" . $dbh->quote($value) . ")";

Doing this ensures that the data in $values will be interpreted correctly, regardless of what quotes appear in $value (unless it contains newline characters). Note that the alternative assignment below does not work!

$stmt = "INSERT INTO SomeTable(SomeColumn) VALUES($dbh->quote($value))";

However, before using $dbh->quote, consider whether to use a placeholder, '?', in instead. You should probably use a placeholder if the string represents a value in the WHERE clause of a SELECT, UPDATE or DELETE statement, or a value in the VALUES list of an INSERT statement, or a value in the SET clause of an UPDATE statement, or a parameter to a function or stored procedure. Note that you must use a placeholder if the string could be longer than 255 characters. Otherwise, the string probably represents a table name or a column name and you must use $dbh->quote.

CREATING STATEMENTS

You can also prepare a statement for multiple uses, and you can do this for SELECT and EXECUTE PROCEDURE statements that return data (cursory statements) as well as noncursory statements that return no data. You create a statement handle (another reference) using:

$sth = $dbh->prepare($stmt);

If the statement is a SELECT that returns data (not SELECT...INTO TEMP) or an EXECUTE PROCEDURE for a procedure that returns values, a cursor is declared for the prepared statement.

According to the DBI specification, the prepare call accepts an optional attributes parameter that is a reference to a hash. At the moment, no parameters are recognized. It would be reasonable to add, for example, {ix_CursorWithHold => 1} to specify that the cursor should be declared WITH HOLD. Similarly, you could add {ix_BlobLocation => 'InFile'} to support per-statement blob location, and {ix_ScrollCursor => 1} to support scroll cursors.

More typically, you need to do error checking, and this is achieved by using:

# Emphasizing the error handling.
die "Failed to prepare '$stmt'\n"
    unless ($sth = $dbh->prepare($stmt));

# Emphasizing the SQL action.
$sth = $dbh->prepare($stmt) or die "Failed to prepare '$stmt'\n"

You can tell whether the statement is just executable or whether it is a cursory (fetchable) statement by testing the (new with Version 0.95) Informix-specific attribute ix_Fetchable. The approved, canonical DBI method of doing this check is "$sth->{NUM_OF_FIELDS} > 0".

Once the statement is prepared, you can execute it:

$sth->execute;

For a noncursory statement, this simply executes the statement. If the statement is executed successfully, the number of rows affected will be returned. If an error occurs, the returned value will be undef. If the statement does not affect any rows, the string returned is "0E0", which evaluates to true but also to zero.

For a cursory statement, $sth->execute opens the cursor. If the cursor is opened successfully, it returns the value "0E0", which evaluates to true but also to zero. If an error occurs, the returned value will be undef.

Although the DBI 0.85 spec is silent on the issue, you can also specify the input parameters for a statement using:

$sth->execute(@parameters);

The first parameter will be supplied as the value for the first place-holder question mark in the statement, the second parameter for the second place-holder, and so on.

Issue: At the moment, there is no checking by DBD::Informix on how many input parameters are supplied and how many are needed. Note that the Informix servers give no support for determining the number of input parameters except in the VALUES clause of an INSERT statement. This needs to be resolved.

Issue: The Informix servers give no support for determining the types of input parameters except in the VALUES clause of an INSERT statement. This means that DBD::Informix cannot handle blobs in the SET clause of an UPDATE statement. The only known way to deal with this is to use a SELECT to retrieve the old data, a DELETE to remove it, and an INSERT to replace it with the modified data. Not nice, but it works.

Warning: Later versions of DBI will specify methods to bind input parameters for statements to Perl variables. This is another area that is subject to change, therefore.

For cursory statements, you can discover the returned column names, types, nullability, and so on. You do this with:

@name = @{$sth->{NAME}};        # Column names
@null = @{$sth->{NULLABLE}};    # True => accepts nulls
@type = @{$sth->{TYPE}};        # ODBC Data Type numbers
@prec = @{$sth->{PRECISION}};   # ODBC PRECISION numbers (or undef)
@scal = @{$sth->{SCALE}};       # ODBC SCALE numbers (or undef)

# Native (Informix) type equivalents
@tnam = @{$sth->{ix_NativeTypeName}};# Type name
@tnum = @{$sth->{ix_ColType}};       # Type number from SysColumns.ColType
@tlen = @{$sth->{ix_ColLength}};     # Type length from SysColumns.ColLength

Note: Informix uses '(expression)' in the array $sth->{NAME} for any nonaliased computed value in a SELECT list, and to describe the return values from stored procedures, and so on. This could be usefully improved. There is also no guarantee that the names returned are unique. For example, in "SELECT A.Column, B.Column FROM Table1 A, Table1 B WHERE ...", both the return columns are described as 'column'.

Note that in versions 0.95 and earlier, the implemented attribute name was ix_NativeTypeNames (plural), as pointed out by Dror Matalon <dror@dnai.com>. This is still supported but is deprecated.

If the statement is a cursory statement, you can retrieve the values in any of a number of ways, as described in the DBI specification.

$ref = $sth->fetchrow_arrayref;
$ref = $sth->fetch;                 # Alternative spelling...
@row = @{$ref};

@row = @{$sth->fetchrow_arrayref};  # Shorthand for above...

@row = $sth->fetchrow_array;

$ref = $sth->fetchall_arrayref;

As usual, you have to worry about whether this worked or not. You would normally, therefore, use:

while ($ref = $sth->fetch)
{
    # We know we got some data here.
    ...
}
# Investigate whether an error occurred or the SELECT
# simply had nothing more to return.
if ($sth->{sqlcode} < 0)
{
    # Process error...
}

The returned data includes blobs mapped into strings. Note that byte blobs might contain ASCII NUL '\0' characters. Perl knows how long the strings are and does preserve NUL in the middle of a byte blob. However, you might need to be careful when you decide how to handle this string.

There is provision to specify how you want blobs handled. You can set the attribute:

$sth->{ix_BlobLocation} = 'InMemory';      # Default
$sth->{ix_BlobLocation} = 'InFile';        # In a named file
$sth->{ix_BlobLocation} = 'DummyValue';    # Return dummy values
$sth->{ix_BlobLocation} = 'NullValue';     # Return undefined

InFile mode returns the name of a file in the fetched array, and that file can be accessed by Perl using normal file access methods. DummyValue mode returns "<<TEXT VALUE>>" for text blobs or "<<BYTE VALUE>>" for byte (binary) blobs. NullValue mode returns undefined (meaning that the Perl "defined" operator would return false) values. Note that these two options do not necessarily prevent the Server from returning the data to the application, but the user does not get to see the data--this depends on the internal implementation of the ESQL/C FETCH operation in conjunction with SQL descriptors.

You can also set the ix_BlobLocation attribute on the database, overriding it at the statement level.

BUG: ix_BlobLocation is not handled properly.

When you have fetched as many rows as required, you close the cursor using:

$sth->finish;

You do not have to finish a cursor explicitly if you executed a fetch that failed to retrieve any data.

Using $sth->finish simply closes the cursor but does not free the cursor or the statement. That is done when you destroy (undef) the statement handle:

undef $sth;

You can also implicitly rebind a statement handle to a new statement by simply using the same variable again. This does not cause any memory leaks.

You can use the ix_StatementText attribute to discover (or rediscover) the text of a statement:

$txt = $sth->{ix_StatementText};

The ix_StatementText attribute has been superseded by the DBI attribute Statement and will be deprecated, starting with Version 0.95.

CURSORS FOR UPDATE

You can use the attribute $sth->{CursorName} to retrieve the name of a cursor. If the statement for $sth is actually a SELECT and the cursor is in a MODE ANSI database or is declared with the 'FOR UPDATE [OF col,...' tag, you can use the cursor name in a 'DELETE...WHERE CURRENT OF' or 'UPDATE...WHERE CURRENT OF' statement.

$st1 = $dbh->prepare("SELECT * FROM SomeTable FOR UPDATE");
$wc = "WHERE CURRENT OF $st1->{CursorName}";
$st2 = $dbh->prepare("UPDATE SomeTable SET SomeColumn = ? $wc");
$st3 = $dbh->prepare("DELETE FROM SomeTable $wc");
$st1->execute;
$row = $st1->fetch;
$st2->execute("New Value");
$row = $st1->fetch;
$st3->execute();

ACCESSING THE SQLCA RECORD

You can access the SQLCA record via either a database handle or a statement handle.

$sqlcode = $sth->{ix_sqlcode};
$sqlerrm = $sth->{ix_sqlerrm};
$sqlerrp = $sth->{ix_sqlerrp};
@sqlerrd = @{$sth->{ix_sqlerrd}};
@sqlwarn = @{$sth->{ix_sqlwarn}};

Note that the warning information is treated as an array (as in Informix 4GL) rather than as a bunch of separate fields (as in Informix ESQL/C). However, the array is indexed from zero (as in ESQL/C, C, Perl, and so on), rather than from one (as in Informix 4GL). Also note that both $sth->{ix_sqlerrd} and $sth->{ix_sqlwarn} return a reference to an array. Inspect the code in the print_sqlca() function in InformixTest.pl for more ideas on the use of these statements. You cannot set the sqlca record.

The sqlerrd array has the following useful columns:

$sth->{ix_sqlerrd}[1] - serial value after insert or ISAM error code
$sth->{ix_sqlerrd}[3] - estimated cost
$sth->{ix_sqlerrd}[4] - offset of the error into the SQL statement
$sth->{ix_sqlerrd}[5] - rowid of the last row processed

OBTAINING THE VALUE INSERTED FOR A SERIAL COLUMN

The following example is a very useful and important technique with Informix. However, it is also not portable to other databases because they do not have the SERIAL data type.

# insert a row into a table with a primary key that is a SERIAL
$stmt = $dbh->do("insert into table (serial_id, number) values(0, 10)");
print "the new row has a serial_id of $sth->{ix_sqlerrd}[1]\n";

For more information, you can read the "Informix ESQL/C Programmer's Manual" or "Informix Guide to SQL: Reference Manual." The exact chapter and verse depends on which version you use.

TRANSACTION MANAGEMENT

Transaction management changed in the DBD::Informix Version 0.56 release, in part because the DBI specification changed. You should read this section carefully. If you find a deviation between what is documented and what actually occurs, be sure to report it. The problem might be in the documentation, in the code, or in both.

Previously, the type of Informix database affected the default AutoCommit attribute. Now the AutoCommit attribute (which can be set in the DBI->connect() call) controls the AutoCommit behavior exclusively.

THE INTERACTIONS OF AUTOCOMMIT WITH INFORMIX DATABASES

Three types of Informix database need to be considered: MODE ANSI, Logged, and UnLogged. Although MODE ANSI databases also have a transaction log, the category of Logged databases specifically excludes MODE ANSI databases. In OnLine, this refers to databases created WITH LOG or WITH BUFFERED LOG; in SE, to databases created WITH LOG IN "/some/file/name".

Two AutoCommit modes exist: On, Off.

Two transaction states are possible: In-TX (In transaction), No-TX (Outside transaction).

At least 13 types of statements (in 4 groups and 9 subgroups) need to be considered:

$drh->connect('xyz');                   # Group 1A
$dbh->do('DATABASE xyz');               # Group 1B
$dbh->do('CREATE DATABASE xyz');        # Group 1B
$dbh->do('ROLLFORWARD DATABASE xyz');   # Group 1B
$dbh->do('START DATABASE xyz');         # Group 1B
$dbh->disconnect();                     # Group 2A
$dbh->do('CLOSE DATABASE');             # Group 2B
$dbh->commit();                         # Group 3A
$dbh->rollback();                       # Group 3A
$dbh->do('BEGIN WORK');                 # Group 3B
$dbh->do('ROLLBACK WORK');              # Group 3C
$dbh->do('COMMIT WORK');                # Group 3C
$dbh->prepare('SELECT ...');            # Group 4A
$dbh->prepare('UPDATE ...');            # Group 4B

Group 1 statements establish connections to databases. The type of database to which you are connected has no effect on the AutoCommit mode. Group 1A is the primary means of connecting to a database; Group 1B statements can change the current database. Group 1B statements, however, cannot be executed except on the ".DEFAULT." connection when you use ESQL/C 6.00 or later.

For all types of databases, the default AutoCommit mode is On. With a MODE ANSI or a Logged database, the value of AutoCommit can be set to Off, which automatically starts a transaction (explicitly if the database is Logged, implicitly if the database is MODE ANSI). For an UnLogged database, the AutoCommit mode cannot be changed. Any attempt to change AutoCommit mode to Off with an UnLogged database generates a nonfatal warning.

Group 2 statements sever the connection to a database. The Group 2A statement renders the database handle unusable; no further operations are possible except 'undef' or reassigning with a new connection. The Group 2B statement means that no operations other than those in Group 1B or 'DROP DATABASE' are permitted on the handle. As with the Group 1B statements, the Group 2B statement can only be used on a ".DEFAULT." connection. The value of AutoCommit is irrelevant after the database is closed but is not altered by DBD::Informix.

Group 3 and 4 statements interact in many complicated ways, but the new style of operation considerably simplifies the interactions. One side effect of the changes is that BEGIN WORK is completely marginalized and will generally cause an error. Although UPDATE is cited in Group 4B, it represents any statement that is not a SELECT statement. Note that 'SELECT...INTO TEMP' is a Group 4B statement because it returns no data to the program. An 'EXECUTE PROCEDURE' statement is in Group 4A if it returns data and in Group 4B if it does not, and you cannot tell which of the two groups applies until after the statement is prepared.

MODE ANSI DATABASES

Previously, MODE ANSI databases were regarded as being in a transaction at all times, but this is not the only way to view the way these databases work. However, it is more satisfactory to regard the state immediately after a database is opened, or immediately after a COMMIT WORK or ROLLBACK WORK operation as being in the No-TX state. Any statement other than a disconnection statement (Group 2) or a commit or rollback (Group 3A or 3C) takes the databases into the In-TX state.

In a MODE ANSI database, you can execute BEGIN WORK successfully. However, if AutoCommit is On, the transaction is immediately committed, so it does you no good.

If the user elects to switch to AutoCommit On, things get trickier. All cursors need to be declared WITH HOLD so that Group 4B statements being committed do not close the active cursors. Whenever a Group 4B statement is executed, the statement needs to be committed. With OnLine (and theoretically with SE), if the statement fails there is no need to do a rollback -- the statement failing did the rollback anyway. As before, the code does ROLLBACK WORK before disconnecting, though it should not actually be necessary.

LOGGED DATABASES

Previously, there were some big distinctions between Logged and MODE ANSI databases. One major advantage of the changes is that now there is essentially no distinction between the two.

Note that executing BEGIN WORK does not buy you anything; you have to switch AutoCommit mode explicitly to get any useful results.

UNLOGGED DATABASES

The transaction state is No-TX and AutoCommit is On, and this cannot be changed. Any attempt to set AutoCommit to Off generates a nonfatal warning but the program will continue; setting AutoCommit to On generates neither a warning nor an error. Both $dbh->commit and $dbh->rollback succeed but do nothing. Executing any Group 3B or 3C statement will generate an error.

Ideally, if you attempt to connect to an UnLogged database with AutoCommit Off, you would get a connect failure. There are problems implementing this because of the way DBI 0.85 behaves when failures occur, so this is not actually implemented.

ATTRIBUTE NAME CHANGES

Early releases of DBD::Informix, some of the Informix-specific attributes had names that did not start 'ix_', but these old-style attribute names are no longer recognized and an error message is generated (by DBI).

MAPPING BETWEEN ESQL/C AND DBD::INFORMIX

A crude form of the mapping between DBD::Informix functions and ESQL/C equivalents follows--there are a number of ways in which it is not quite precise (for example, the influence of AutoCommit), but the mapping is accurate enough for most purposes.

DBI->connect            => DATABASE in 5.0x
$dbh->disconnect        => CLOSE DATABASE in 5.0x

DBI->connect            => CONNECT in 6.0x and later
$dbh->disconnect        => DISCONNECT in 6.0x and later

$dbh->commit            => COMMIT WORK (+BEGIN WORK)
$dbh->rollback          => ROLLBACK WORK (+BEGIN WORK)

$dbh->do                => EXECUTE IMMEDIATE
$dbh->prepare           => PREPARE, DESCRIBE (DECLARE)
$sth->execute           => EXECUTE or OPEN
$sth->fetch             => FETCH
$sth->fetchrow          => FETCH
$sth->finish            => CLOSE

undef $sth              => FREE cursor, FREE statement, etc

KNOWN RESTRICTIONS

Blobs can be reliably located only in memory.
If you use Informix ESQL/C Version 6.00 or later and do not set both the environment variables CLIENT_LOCALE and DB_LOCALE, ESQL/C might set one or both of them during the connect operation. When ESQL/C does so, it makes Perl emit a "Bad free()" error if you subsequently modify the %ENV hash in the Perl script. This is nasty, but there is no easy solution. To establish what values you should set, arrange for the compilation to define DBD_IX_DEBUG_ENVIRONMENT:
```
make UFLAGS=-DDBD_IX_DEBUG_ENVIRONMENT
```
The code in dbdimp.ec will then call the function dbd_ix_printenv() in dbd_ix_db_login(), which will help you identify what has been changed.
Blobs cannot yet be updated by DBD::Informix (mainly because ESQL/C does not readily provide the information needed for updating blobs).

AUTHOR

At various times:

Tim Bunce (Tim.Bunce@ig.co.uk)
Alligator Descartes (descarte@hermetica.com) # Obsolete email address
Alligator Descartes (descarte@arcana.co.uk) # Obsolete email address
Alligator Descartes (descarte@symbolstone.org)
Jonathan Leffler (johnl@informix.com) # Obsolete email address
Jonathan Leffler (jleffler@visa.com) # Obsolete email address
Jonathan Leffler (j.leffler@acm.org)
Jonathan Leffler (jleffler@informix.com)

With contributions from many other people who should all be mentioned in the ChangeLog file.

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