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.
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.
The DBD::XBase module supports dBaseIII and IV and Fox* flavors of dbf files, including their dbt and fpt memo files.
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.
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.
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 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).
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.
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?
Can the default format be changed? If so, how (both for a single expression in an sql statement, and as a database connection default)?
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?
What kinds of date and time arithmetic and functions are supported?
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?
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?
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.
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?
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?
Does the driver support type_info method?
The DBD::XBase driver supports the type_info method.
Does the database support transactions?
DBD::XBase does not support transactions.
If so, what is the default transaction isolation level?
What other isolation levels are supported and how can they be enabled per-connection or per-transaction?
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 ...".
How can a select statement be modified to lock the selected rows from being changed by another transaction. E.g., "select ... for update".
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.
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?
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.
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.
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?
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.
Can you select a row-numbering pseudocolumn and if so, what is it called?
DBD::XBase does not support a row-numbering pseudocolumn.
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?
Do unsupported values of the TYPE attribute generate a warning?
What syntax is used to call stored procedures and, where possible, get results?
Stored procedures are not applicable in the XBase format.
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.
XXX expand description
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).
Does the driver support positioned updates and deletes (also called updatable cursors)? If so, what syntax is used? E.g, "update ... where current of $cursor_name".
DBD::XBase does not support positioned updates or deletes.
List any significant differences in behaviour from the current DBI specification.
DBD::XBase has no known significant differences in behaviour from the current DBI specification.
Does the driver allow multiple concurrent database connections to the same database?
DBD::XBase supports an unlimited number of concurrent database connections to one or more databases.
Does the driver allow a new statement handle to be prepared and used while still fetching data from another statment handle associated with the same database handle?
DBD::XBase supports the preparation and execution of a new statement handle while still fetching data from another statment handle associated with the same database handle.
What generally useful private ($h->func(...)) methods are provided?
DBD::XBase has no generally useful private methods.
Adding :1 style of placeholders; handling numbers outside of Perl's numeric range.
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.
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.
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.
Yes? No? Yes but the driver hides this by re-preparing as needed?
N/A, only AutoCommit mode is supported.
Like Ingperl, Oraperl etc
No emulation layers are supported.
|| or + or CONCAT() or what?
String concatenation is not supported.
NUM_OF_FIELDS is set by execute.
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.