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 via his e-mail email@example.com or the dbi-(dev|users) mailing lists.
The DBD::XBase module supports dBaseIII and IV and Fox* flawors 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 dbt 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?
Generic NUMBER(p,s) and FLOAT(p,s), INTEGER(l). Maximul scale and precision unknown, resp. limited by Perl's handling of numbers. In the dbf files, the numbers are stored as ASCII strings, or binary integers or floats.
Numbers are always returned converted to numbers, so numbers outside of Perl's valid range are not possible (even if this restriction might be withdrawn in the future).
Does the database and driver support numbers outside the valid range for perl numbers?
Are numbers returned as strings in this case?
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. No charset options are recongnized.
What is the maximum size for each type?
65535 characters (even if the older dBase's only allowed 255 characters, so created dbf might not be porteble to other xbase-like software).
Are any types blank padded? If so which, e.g., CHAR.
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?
No (there is no notion of charsets).
What date, time and date+time data types are supported and what is their valid range and resolution?
Default (and only possible) date format for input and output is 8 char string 'YYYYMMDD'. DBD::XBase doesn't check for validity of this string.
The datetime type works internally with the precision up to 1/1000 s. DBD::XBase currently supports this using Un*x standard seconds-since-epoch value (possibly with decimal part). This might change in the future.
What date, time and date+time formats are supported?
No formats except the defaults are supported.
What is the default output format for each?
'YYYYMMDD' and number of seconds since 1970/1/1.
What is the default input format for each? Are multiple input format recognised?
'YYYYMMDD' and number of seconds since 1970/1/1. This is the only possibility.
If only part of a date is specified, how does the rest default?
No partial definitions are allowed.
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 zones handling.
What LONG/BLOB data types does the database support? (LONG, LONG RAW, CLOB, BLOB, BFILE etc) What are their maximum sizes?
BLOB/MEMO data types are supported. With dBaseIII dbt files, the memo field cannot contain \x1a byte, with dBaseIV and Fox* dbt/fpt's any value can be stored.
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?
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?
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).
If equi-joins are supported but don't use the standard "WHERE a.field = b.field" syntax, then describe the syntax. Are 'outer joins' supported, if so with what syntax?
What is the max size of table names? And column names?
For table names limited by OS's max filename length. For column name 11 characters.
What characters are valid without quoting?
It has to start with letter and 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?
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 (case sensitively), column names as uppoercase.
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.
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?
Can you select a row-numbering pseudocolumn and if so, what is it called?
Is parameter binding supported by the database, emulated by the driver or not supported at all?
Parameter binding is emulated by the driver.
If parameter binding is supported, is the :1 placeholder style also 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?
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?
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.
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 any row cache.
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?