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CXXXIX. SESAM Database Functions
SESAM/SQL-Server is a mainframe database system, developed by
Fujitsu Siemens Computers, Germany. It runs on high-end mainframe
servers using the operating system BS2000/OSD.
In numerous productive BS2000 installations, SESAM/SQL-Server has
proven
the ease of use of Java-, Web- and client/server connectivity,
the capability to work with an availability of more than
99.99%,
the ability to manage tens and even hundreds of thousands of
users.
There is a PHP 3 SESAM interface available which allows
database operations via PHP-scripts.
Note:
Access to SESAM is only available with the latest CVS-Version of
PHP 3. PHP 4 does not support the SESAM database.
The behaviour of these functions is affected by settings in php.ini.
- sesam_oml
string
Name of BS2000 PLAM library containing the loadable SESAM
driver modules. Required for using SESAM functions. The
BS2000 PLAM library must be set ACCESS=READ,SHARE=YES
because it must be readable by the apache server's user id.
- sesam_configfile
string
Name of SESAM application configuration file. Required for
using SESAM functions. The BS2000 file must be readable by
the apache server's user id.
The application configuration file will usually contain a
configuration like (see SESAM
reference manual):
- sesam_messagecatalog
string
Name of SESAM message catalog file. In most cases, this
directive is not necessary. Only if the SESAM message file
is not installed in the system's BS2000 message file table,
it can be set with this directive.
The message catalog must be set ACCESS=READ,SHARE=YES because
it must be readable by the apache server's user id.
There is no standalone support for the PHP SESAM interface, it
works only as an integrated Apache module. In the Apache PHP
module, this SESAM interface is
configured using Apache directives.
Table 1. SESAM Configuration directives | Directive | Meaning |
|---|
| php3_sesam_oml |
Name of BS2000 PLAM library containing the loadable SESAM
driver modules. Required for using SESAM functions.
Example:
| | php3_sesam_configfile |
Name of SESAM application configuration file. Required for
using SESAM functions.
Example:
It will usually contain a configuration like (see SESAM
reference manual):
| | php3_sesam_messagecatalog |
Name of SESAM message catalog file. In most cases, this
directive is not necessary. Only if the SESAM message file
is not installed in the system's BS2000 message file table,
it can be set with this directive.
Example:
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In addition to the configuration of the PHP/SESAM interface, you
have to configure the SESAM-Database server itself on your
mainframe as usual. That means:
starting the SESAM database handler (DBH), and
connecting the databases with the SESAM database handler
To get a connection between a PHP script and the database
handler, the CNF and NAM
parameters of the selected SESAM configuration file must match
the id of the started database handler.
In case of distributed databases you have to start a
SESAM/SQL-DCN agent with the distribution table including the
host and database names.
The communication between PHP (running in the POSIX subsystem)
and the database handler (running outside the POSIX subsystem) is
realized by a special driver module called SQLSCI and SESAM
connection modules using common memory. Because of the common
memory access, and because PHP is a static part of the web
server, database accesses are very fast, as they do not require
remote accesses via ODBC, JDBC or UTM.
Only a small stub loader (SESMOD) is linked with PHP, and the
SESAM connection modules are pulled in from SESAM's OML PLAM
library. In the configuration, you must tell PHP
the name of this PLAM library, and the file link to use for the
SESAM configuration file (As of SESAM V3.0, SQLSCI is available
in the SESAM Tool Library, which is part of the standard
distribution).
Because the SQL command quoting for single quotes uses duplicated
single quotes (as opposed to a single quote preceded by a
backslash, used in some other databases), it is advisable to set
the PHP configuration directives php3_magic_quotes_gpc
and php3_magic_quotes_sybase
to On for all PHP scripts using the SESAM
interface.
Because of limitations of the BS2000 process model, the driver
can be loaded only after the Apache server has forked off its
server child processes. This will slightly slow down the initial
SESAM request of each child, but subsequent accesses will respond
at full speed.
When explicitly defining a Message Catalog for SESAM, that
catalog will be loaded each time the driver is loaded (i.e., at
the initial SESAM request). The BS2000 operating system prints a
message after successful load of the message catalog, which will
be sent to Apache's error_log file. BS2000 currently does not
allow suppression of this message, it will slowly fill up the
log.
Make sure that the SESAM OML PLAM library and SESAM configuration
file are readable by the user id running the web server.
Otherwise, the server will be unable to load the driver, and will
not allow to call any SESAM functions. Also, access to the
database must be granted to the user id under which the Apache
server is running. Otherwise, connections to the SESAM database
handler will fail.
The result cursors which are allocated for SQL "select type"
queries can be either "sequential" or "scrollable". Because of
the larger memory overhead needed by "scrollable" cursors, the
default is "sequential".
When using "scrollable" cursors, the cursor can be freely
positioned on the result set. For each "scrollable" query, there
are global default values for the scrolling type (initialized to:
SESAM_SEEK_NEXT) and the scrolling offset
which can either be set once by
sesam_seek_row() or each time when fetching a
row using sesam_fetch_row(). When fetching a
row using a "scrollable" cursor, the following post-processing is
done for the global default values for the scrolling type and
scrolling offset:
Table 2. Scrolled Cursor Post-Processing | Scroll Type | Action |
|---|
| SESAM_SEEK_NEXT | none | | SESAM_SEEK_PRIOR | none | | SESAM_SEEK_FIRST |
set scroll type to SESAM_SEEK_NEXT
| | SESAM_SEEK_LAST |
set scroll type to SESAM_SEEK_PRIOR
| | SESAM_SEEK_ABSOLUTE | Auto-Increment internal offset value | | SESAM_SEEK_RELATIVE | none. (maintain global default
offset value, which allows for, e.g., fetching
each 10th row backwards)
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Because in the PHP world it is natural to start indexes at zero
(rather than 1), some adaptions have been made to the SESAM
interface: whenever an indexed array is starting with index 1 in
the native SESAM interface, the PHP interface uses index 0 as a
starting point. E.g., when retrieving columns with
sesam_fetch_row(), the first column has the
index 0, and the subsequent columns have indexes up to (but not
including) the column count ($array["count"]). When porting
SESAM applications from other high level languages to PHP, be
aware of this changed interface. Where appropriate, the
description of the respective PHP sesam functions include a note
that the index is zero based.
When allowing access to the SESAM databases, the web server user
should only have as little privileges as possible. For most
databases, only read access privilege should be granted.
Depending on your usage scenario, add more access rights as you
see fit. Never allow full control to any database for any user
from the 'net! Restrict access to PHP scripts which must
administer the database by using password control and/or SSL
security.
No two SQL dialects are ever 100% compatible. When porting
SQL applications from other database interfaces to SESAM,
some adaption may be required. The following typical
differences should be noted:
Vendor specific data types
Some vendor specific data types may have to be replaced by
standard SQL data types (e.g., TEXT could
be replaced by VARCHAR(max. size)).
Keywords as SQL identifiers
In SESAM (as in standard SQL), such identifiers must be
enclosed in double quotes (or renamed).
Display length in data types
SESAM data types have a precision, not a display
length. Instead of int(4) (intended use:
integers up to '9999'), SESAM requires simply
int for an implied size of 31 bits. Also,
the only datetime data types available in SESAM are:
DATE, TIME(3) and
TIMESTAMP(3).
SQL types with vendor-specific unsigned,
zerofill, or
auto_increment attributes
Unsigned and zerofill
are not supported. Auto_increment is
automatic (use "INSERT ... VALUES(*, ...)"
instead of "... VALUES(0, ...)" to take
advantage of SESAM-implied auto-increment.
int ... DEFAULT '0000'
Numeric variables must not be initialized with string
constants. Use DEFAULT 0 instead. To
initialize variables of the datetime SQL data types, the
initialization string must be prefixed with the respective
type keyword, as in: CREATE TABLE exmpl ( xtime
timestamp(3) DEFAULT TIMESTAMP '1970-01-01 00:00:00.000' NOT
NULL );
$count = xxxx_num_rows();
Some databases promise to guess/estimate the number of the
rows in a query result, even though the returned value is
grossly incorrect. SESAM does not know the number of rows in
a query result before actually fetching them. If you REALLY
need the count, try SELECT COUNT(...) WHERE
..., it will tell you the number of hits. A second
query will (hopefully) return the results.
DROP TABLE thename;
In SESAM, in the DROP TABLE command, the
table name must be either followed by the keyword
RESTRICT or
CASCADE. When specifying
RESTRICT, an error is returned if there are
dependent objects (e.g., VIEWs), while with
CASCADE, dependent objects will be deleted
along with the specified table.
SESAM does not currently support the BLOB type. A future version
of SESAM will have support for BLOB.
At the PHP interface, the following type conversions are
automatically applied when retrieving SQL fields:
Table 3. SQL to PHP Type Conversions | SQL Type | PHP Type |
|---|
| SMALLINT, INTEGER | integer | | NUMERIC, DECIMAL, FLOAT, REAL, DOUBLE | float | | DATE, TIME, TIMESTAMP | string | | VARCHAR, CHARACTER | string |
When retrieving a complete row, the result is returned as an
array. Empty fields are not filled in, so you will have to check
for the existence of the individual fields yourself (use
isset() or empty() to test
for empty fields). That allows more user control over the
appearance of empty fields (than in the case of an empty string
as the representation of an empty field).
The special "multiple fields" feature of SESAM allows a column to
consist of an array of fields. Such a "multiple field" column can
be created like this:
Example 1. Creating a "multiple field" column CREATE TABLE multi_field_test (
pkey CHAR(20) PRIMARY KEY,
multi(3) CHAR(12)
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and can be filled in using:
Example 2. Filling a "multiple field" column INSERT INTO multi_field_test (pkey, multi(2..3) )
VALUES ('Second', <'first_val', 'second_val'>) |
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Note that (like in this case) leading empty sub-fields are
ignored, and the filled-in values are collapsed, so that in the
above example the result will appear as multi(1..2) instead of
multi(2..3).
When retrieving a result row, "multiple columns" are accessed
like "inlined" additional columns. In the example above, "pkey"
will have the index 0, and the three "multi(1..3)" columns will
be accessible as indices 1 through 3.
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shm_remove
