File: driver_characteristics

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=head1 Database and Driver Characteristics

This document is designed to give you a flavour of the functionality
and quirks of the different DBI drivers and their databases.

The line between the functionality and quirks of a given driver and the
functionality and quirks of its corresponding database is blurred. In
some cases the database has functionality that the driver can't or
doesn't access, in others the driver may emulate functionality that the
database doesn't support, like placeholders. So when you see the terms
driver and database below, take them with a pinch of salt.

We don't attempt to describe the drivers and database in full detail
here, we're only interested in the key features that are most commonly
used. And for those features we're just providing an outline guide.
Consult the database documentation for full details.

The primary goals are:

  - to provide a simple overview of each driver and database.
  - to help you initially select a suitable DBI driver and database.
  - to help you quickly identify potential issues if you need to port
     an application from one driver and database to another.

=head2 Driver Name, Version, Author and Contact Details

This driver summary is for DBD::XBase version 0.130.

The driver author is Jan Pazdziora and he can be contacted at
jpx dash perl at adelton dot com.

=head2 Supported Database Versions and Options

The DBD::XBase module supports dBaseIII and IV and Fox* flavors of
dbf files, including their dbt and fpt memo files.


=head2 Connect Syntax

     Details of the syntax of the dsn including any optional parts.

The DBI->connect Data Source Name (DSN) should include the directory
where the dbf files are located as the third part.

  dbi:XBase:/path/to/directory

It defaults to current directory.

     Details of any driver specific attributes applicable to the
     connect method.

There are no driver specific attributes for the DBI->connect method.


=head2 Numeric Data Handling

     What numeric data types do the database and driver support? (INTEGER,
     FLOAT, NUMBER(p,s) etc).  What is the maximum scale and precision for
     each type?

DBD::XBase supports generic NUMBER(p,s), FLOAT(p,s) and INTEGER(l)
types. Maximul scale and precision unknown, limited by Perl's handling
of numbers. In the dbf files, the numbers are stored as ASCII strings,
or binary integers or floats.

Existing dbf files come with the field types defined in the dbf file
header. Numeric types can be either stored as ASCII string or in some
binary format. DBD::XBase (via XBase.pm) parses this information and reads and
writes the fields in that format.

When you create a I<new> dbf file (via CREATE TABLE), the numeric
fields are always created in the traditional XBase way, as an ASCII
string.  (The XBase.pm module offer more control over this.)

     Does the database and driver support numbers outside the valid range
     for perl numbers?
     Are numbers returned as strings in this case?

Numeric fields are always returned as perl numeric values, not strings,
so numbers outside of Perl's valid range are not possible (this
restriction might be withdrawn in the future).


=head2 String Data Handling

     What string data types does the database support? (CHAR, VARCHAR, etc)

DBD::XBase knows CHAR(length) and VARCHAR(length), both are stored as
fixed length chars however. These can contain any binary values.

     What is the maximum size for each type?

The maximum length is 65535 characters for both types (even if the
older dBase's only allowed 255 characters, so created dbf might not be
portable to other xbase compatible software).

     Are any types blank padded? If so which, e.g., CHAR.

Both CHAR and VARCHAR are blank padded (unless ChopBlanks set).

     How does the database handle data with the 8th bit set (national
     language character sets etc)?

Data with the 8th bit set are handles transparently, no national
language character set conversions are done.

     Is Unicode supported?

Since the string types can store binary data, Unicode strings can be
stored.


=head2 Date Data Handling

     What date, time and date+time data types are supported
     and what is their valid range and resolution?

     What is the default output format for each?

     What is the default input format for each?
     Are multiple input format recognised?

DBD::XBase supports these date and time types:

  DATE
  DATETIME
  TIME

The DATE type holds an eight character string in the format
`YYYYMMDD'.  Only that format can be used for input and output.
DBD::XBase doesn't check for validity of the values.

The DATETIME and TIME types store (internally) a 4 byte integer day
value (Julian Day System) and a 4 byte integer seconds value (that
counts 1/1000's of a second since midnight).  DBD::XBase inputs and
outputs these types using a floating point unix-style
seconds-since-epoch value (possibly with decimal part and possibly
negative). This might change in the future.


     If only part of a date is specified, how does the rest default?

     If two digit years can be used, how is the century determined?

N/A

     Can the default format be changed? If so, how (both for a single
     expression in an sql statement, and as a database connection default)?

No.

     How can I get the current date+time in an SQL expression?

There is no way to get the current date/time.

     How can I input date and date+time values in other formats?

     How can I output date and date+time values in other formats?

N/A

     What kinds of date and time arithmetic and functions are supported?

None.

     What SQL expression can be used to convert from an integer "seconds
     since 1-jan-1970 GMT" value to the corresponding database date+time?
     If not possible, then what perl expression can be used?

N/A

     What SQL expression can be used to convert from a database date+time
     value into the corresponding "seconds since 1-jan-1970 GMT" value?
     If not possible, then what perl expression can be used?

N/A

     How does the database deal with time zones, especially where the
     client inserting a date, the server and a client reading the date
     are all in different time zones?

There is no time zone handling.


=head2 LONG/BLOB Data Handling

     What LONG/BLOB data types does the database support?
     (LONG, LONG RAW, CLOB, BLOB, BFILE etc)

DBD::XBase supports a MEMO data type. BLOB can be used as an alias for
MEMO.

With dBaseIII dbt files, the memo
field cannot contain \x1a byte, with dBaseIV and Fox* dbt/fpt's any
value can be stored.

     What are their maximum sizes?

At least 2 GB are possible for all types of memo files.

     Which types, if any, must be passed to and from the database as pairs
     of hex digits?

N/A

     Do the LongReadLen and LongTruncOk attributes work as defined?
     What is the maximum value, if any, for LongReadLen?

The LongReadLen and LongTruncOk attributes are ignored/are broken
(will be fixed).

     Is special handling required for some or all LONG/BLOB data types?

N/A


=head2 Other Data Handling issues

     Does the driver support type_info method?

The DBD::XBase driver supports the type_info method.


=head2 Transactions and Transaction Isolation

     Does the database support transactions?

DBD::XBase does not support transactions.

     If so, what is the default transaction isolation level?

N/A

     What other isolation levels are supported and how can they
     be enabled per-connection or per-transaction?

N/A


=head2 Explicit Locks

     What is the default locking behaviour for reading and writing?

DBD::XBase does not lock the tables (files) it is working on.
(Hopefully some mechanism will be provided in the future.)

     What statements can be used to explicitly lock a table with
     various types/levels of lock? E.g., "lock table ...".

N/A

     How can a select statement be modified to lock the selected rows
     from being changed by another transaction.
     E.g., "select ... for update".

N/A


=head2 No-Table Expression Select Syntax

     What syntax is used for 'selecting' a constant expression
     from the database? E.g., "select 42 from dual" (Oracle).

You can't select a constant expression using DBD::XBase. Only
table field names, or * for all, can be selected.


=head2 Table Join Syntax

     If equi-joins are supported but don't use the standard
     "WHERE a.field = b.field" syntax, then describe the syntax.

DBD::XBase does not support table joins.

     Are 'outer joins' supported, if so with what syntax?

N/A


=head2 Table and Column Names

     What is the max size of table names? And column names?

The XBase format stores each table as a distinct file. The
table names are limited by filesystem's maximum filename length.

Column names are limited to 11 characters.

     What characters are valid without quoting?

Table and field names have to start with letter, a combination of
letters, digits and underscores may follow.

     Can table and field names be quoted? If so, how?
     What characters are valid with quoting?

DBD::XBase does not support putting quotes around table or column names.

     Are table/column names stored as uppercase, lowercase or
     as-entered?
     Are table/column names case sensitive?

Table names are stored and treated as entered. The case sensitivity
depends on the filesystem that the file is stored on.  Column names are
stored as uppercase and are not case sensitive.

     Can national character sets (with the 8th bit set) be used?

National character sets can be used.


=head2 Case sensivity of like operator

     Is the LIKE operator case sensitive?
     If so, how can case insensitive LIKE operations be performed?

The LIKE operator is not case sensitive. There is (currently) no case
sensitive operator.


=head2 Row ID

     If the database supports a 'row id' pseudocolumn, what is
     it called? E.g., 'rowid' in Oracle, 'tid' in Ingres.

DBD::XBase does not support a 'row id' pseudocolumn.

     Can it be treated as a string when fetching and reusing in
     later statements? If not, what special handling is required?

N/A


=head2 Automatic Key or Sequence Generation

     Does the database offer automatic key generation such as
     'auto increment' or 'system generated' keys?

     Does the database support sequence generators?
     If so, what syntax is used?

DBD::XBase does not support automatic key generation or sequence
generators owing to the limitations of the XBase format.


=head2 Automatic Row Numbering and Row Count Limiting

     Can you select a row-numbering pseudocolumn and if so, what
     is it called?

DBD::XBase does not support a row-numbering pseudocolumn.


=head2 Parameter binding

     Is parameter binding supported by the database, emulated by the
     driver or not supported at all?

Parameter binding is implemented in the driver.

     If parameter binding is supported, is the :1 placeholder style also
     supported?

The :1 placeholder style is not (yet) supported.

     Does the driver support the TYPE attribute do bind_param?
     If so, which types are supported and how do they affect the bind?

No.

     Do unsupported values of the TYPE attribute generate a warning?

N/A


=head2 Stored procedures

     What syntax is used to call stored procedures and, where possible,
     get results?

Stored procedures are not applicable in the XBase format.


=head2 Table Metadata

     Does the driver support table_info method?

DBD::XBase supports the table_info method.

     How can detailed information about the columns of a table be fetched?

There si no way to get that information (at the moment).

     How can detailed information about the indexes of a table be fetched?

Indexes are not supported.

     How can detailed information about the keys of a table be fetched?

Keys are not supported.


=head2 Driver-specific database handle attributes

xbase_ignorememo.

XXX expand description


=head2 Driver-specific statement handle attributes

xbase_ignorememo.


=head2 Default local row cache size and behaviour

     Does the driver or database implement a local row cache when fetching
     rows from a select statement? What is the default size?

DBD::XBase doesn't maintain a row cache (not applicable since the data
file is local to the driver).


=head2 Positioned updates and deletes

     Does the driver support positioned updates and deletes (also called
     updatable cursors)?  If so, what syntax is used? E.g, "update ...
     where current of $cursor_name".

DBD::XBase does not support positioned updates or deletes.


=head2 Differences from the DBI specification

     List any significant differences in behaviour from the current DBI
     specification.

DBD::XBase has no known significant differences in behaviour from the
current DBI specification.


=head2 URLs to more database/driver specific information

  http://www.clicketyclick.dk/databases/xbase/format/


=head2 Multiple concurrent database connections

     Does the driver allow multiple concurrent database connections
     to the same database?

DBD::XBase supports an unlimited number of concurrent database
connections to one or more databases.


=head2 Concurrent use of multiple statement handles from same $dbh.

     Does the driver allow a new statement handle to be prepared and used
     while still fetching data from another statment handle associated
     with the same database handle?

DBD::XBase supports the preparation and execution of a new statement
handle while still fetching data from another statment handle
associated with the same database handle.


=head2 Driver specific methods

     What generally useful private ($h->func(...)) methods are provided?

DBD::XBase has no generally useful private methods.


=head2 Future Changes Planned for the Driver

Adding :1 style of placeholders; handling numbers outside of Perl's
numeric range.

=head2 How to get value of auto-increment field
 
        If your database supports some kind of auto-increment key
        then how can a script get the value of the key used for
        the most recent insert statement?

DBD::XBase does not support auto-increment keys.

=head2 Auto conversion of numbers to strings and strings to numbers?

        Does your database automatically convert strings to numbers
        and number to strings as needed? E.g. does
                INSERT INTO foo (num_field, str_field) VALUES ('42',42)
        work? If not, what type conversion functions are needed.
 
Yes, DBD::XBase automatically converts between strings and numbers.

=head2 And strings to date and dates to strings?

        Does your database automatically convert strings to dates
        and dates to strings as needed? E.g. does
                INSERT INTO foo (date_field) VALUES ('...date string...')
        work? If not, what type conversion functions are needed.

Yes, DBD::XBase automatically converts between dates and strings.

=head2 Which character types can store embedded nulls?

        Any? None?

Any.

=head2 Does commit close/finish all prepared statements?

        Yes? No? Yes but the driver hides this by re-preparing as needed?

N/A, only AutoCommit mode is supported.

=head2 Are any emulations of other interfaces supplied?

        Like Ingperl, Oraperl etc

No emulation layers are supported.

=head2 String concatenation operator

        || or + or CONCAT() or what?

String concatenation is not supported.

=head2 NUM_OF_FIELDS set by prepare or execute?

        Which?

NUM_OF_FIELDS is set by execute.

=head2 Other Significant Database Features

        This is where you get a chance to 'sell' your database and driver.
        What's most important to most potential perl DBI users?

It's a lovely piece of software, especially when you have to deal with
dbf files.

=cut